The avant-garde probably never looked as moderate and conservative as it did in 1888, when a group of young, bearded French painters founded a group known as "Les Nabis." The facial hair was not incidental either, helping to give the group its moniker: "Nabi" is Hebrew for prophet; the joke being that these painters resembled, in their fervor and hirsute appearance, the Biblical prophets.

Along with Pierre Bonnard and Edouard Vuillard, one of the group's leading lights was Maurice Denis, whose art is now the subject of an exhibition at the high-rise Sompo Japan Museum of Art in Tokyo's central Shinjuku district.

The first problem people have with Les Nabis as an avant-garde group is finding anything overtly cutting-edge or radical about their work. In fact, the artworks seem aimed more at prettiness and gentle harmony than the artistic rebellion, shock of the new, or general rocking of the boat that is associated with the avant-garde.

That is certainly true of this exhibition, which focuses on domestic and family scenes by Denis. The works selected evoke an idyllic world, in which well-fed infants are constantly dandled and fondled by doting mothers amid well-furnished, bourgeois backdrops.

Not only this, but there seems to be something of a trajectory: "La Toilette de l'enfant" (1899) is a tender treatment by the artist of his wife and baby daughter, but "Grand portrait de famille" (1902) from a few years later shows the same mother now surrounded by three angelic offspring, and happier than ever.

It may be a coincidence, but in the period before World War I, there was great concern in France about the stagnant French population vis-a-vis the perceived rising hordes of neighboring, heavily-militarized Germany. In this context Denis' "Grand portrait de famille" almost seems like an advert for having larger families in the future national interest.

Another key element to emerge at the exhibition is Denis' strong Christian faith. This can be seen in several oil paintings, such as "Hommage a l'enfant Jesus" (1905), and most effectively in "La Vierge au baiser" (The Madonna of the kiss), a love-suffused design in distemper for a stained-glass window.

Such aspects — the family man, Christian faith, art that wouldn't look out of place in a chapel or on a biscuit tin — is something of a mismatch with our typical idea of the avant-garde artist: a Van Gogh, Egon Schiele or Modigliani, some sort of syphilitic revolutionary maniacally reformulating the art paradigm from his impoverished garret as the bourgeois world stares on uncomprehendingly.

Not only was Denis one of the chief painters of Les Nabis, he was also among its main theorists. But even the statements of the movement seem to lack any real avant-garde fire. Denis' most famous aphorism sounds rather like a statement of the obvious.

"It should be remembered that a picture — before being a warhorse, a nude, or an anecdote of some sort — is essentially a flat surface covered with colors assembled in a certain order," he solemnly announced during the early years of the movement.

But innocuous as it sounds, this simple statement represented a radical break with the tradition that Western art had followed since the Renaissance, when the Italian polymath Leon Battista Alberti, in his treatise "On Painting," formulated the ideas of using perspective and optics to create paintings that existed as imaginary windows into scenes.

Rather than pretending to stare into three-dimensional space, Les Nabis embraced the flatness of the canvas and focused on painting as an act of decoration rather than illusionism. This is what gives their art its sweet harmonic qualities. Things are arranged for visual rather than illusionary effect. Focusing on the way in which color and shapes covered the canvas heightened the decorative possibilities of painting and proved a major influence on artists such as Henri Matisse and many subsequent avant-garde movements.

A good example of Les Nabis' principles is the impressive "Portrait des enfants Kapferer" (1919). Although painted after the original group had disbanded, this portrait of two young children is still dominated by the desire to include a range of visually pleasing elements in the composition, to the extent that the principals, the children themselves, are almost reduced to incidentals. After a cursory glance at them, we take in the patterns on the carpet and chair; the toys strewn decorously around; and the children's pet cat, placed atop a chair like a carved decoration.

Quietly revolutionary as they were, however, Les Nabis also lacked that other quality of true avant-gardists: the fanaticism of their convictions. Having broken the mold they also seemed keen to patch things up again. In "Portrait des enfants Kapferer," we get a sense of Denis being drawn back to the illusionist tricks of Alberti, with a large mirror behind the chair affording us a discrete glimpse of the children's doting parents in the background.

"The Exhibition of the work of Maurice Denis" at the Sompo Japan Museum of Art runs till Nov. 13, admission ¥1,000, open 10 a.m.-6 p.m., closed Mon. For more information, visit www.sompo-japan.co.jp/museum/english.