Competition is intensifying in Japan over a new breed of portable digital-audio players that allows music lovers to carry around a vast library of their favorite tracks.

Posing a serious challenge to Apple Computer Inc.'s iPod, Sony Corp. earlier this month launched its latest Walkman model, featuring a large-capacity hard-disk drive.

But Apple is unlikely to relinquish its dominance easily; it will release its popular iPod mini, a smaller version of the iPod, in markets outside the U.S. on Saturday.