Moody's Investors Service Inc. said Monday that it has changed its rating outlook for Mitsui Mutual Life Insurance Co. to negative from stable, due to increased uncertainty over Japan's life insurance industry as a whole.

The Baa3 insurance financial strength rating of Mitsui Mutual was left unchanged, however, the U.S. credit rating agency said.

The slumping stock market and intensified competition are pressing Japanese life insurers with weaker capital bases, such as Mitsui Mutual, which, although recently given support by other Mitsui group firms, has faced a decline of policies in force since fiscal 1997, Moody's said.