Sony Corp. said Thursday it will release on July 10 a Walkman portable music player that can store up to 13,000 songs, a move expected to pose a serious challenge to Apple Computer Inc.'s iPod, a dominant leader in the field.

The plan was unveiled on the occasion of the Walkman's 25th anniversary. The upgraded Walkman is the first to feature a hard-disk drive in its vast lineup, which started as a cassette-tape player and has expanded to include CD, MD and flash memory.

With large storage capacity, a hard-disk drive player allows users to carry around a vast music collection.