Apple Computer Inc.'s iPod digital music and video players have been an explosive hit in the United States and Japan, but sales of the product may be eventually hampered by the complicated copyright system here.

In the United States, the idea of carrying around TV sitcoms or dramas in a portable player and watching them anywhere has been widely accepted, and Apple wants to spread that concept to the rest of the world.

But the Japanese copyright system may impede the spread of the portable digital audio and video players in this country. IPod-type devices had a 60 percent share of the market as of early November, and sales are rising rapidly.