Translation guide
A portable cassette or media player, originally a Sony brand. In Japanese, it is a trademarked name commonly used generically.
ウォークマン
Walkman (Sony brand)
Referring to a portable audio player, especially the classic Sony Walkman.
The standard term, derived from the Sony brand. Used for both original cassette players and later digital models.
彼はまだウォークマンでカセットテープを聴いている。
He still listens to cassette tapes on his Walkman.
Generic term for any portable media player, not brand-specific.
新しいポータブルプレーヤーを買った。
I bought a new portable player.
ウォークマン is a registered trademark of Sony, but it is often used generically in Japanese to refer to any portable cassette player. For modern digital audio players, ポータブルプレーヤー or specific terms like iPod are more common.