TOKYO — Sony is sending its cassette tape Walkman into retirement in Japan as demand for a music player that was ground-breaking in its day dwindles to a tiny niche in the era of digital technology.

Sony stopped Japanese production of the portable music player in April and sales will end once the last batch disappears from stores, company spokeswoman Hiroko Nakamura said Monday.

Sony has sold 220 million cassette Walkman players globally since the product’s July 1979 debut that changed lifestyles by popularizing music on the go.

More than 30 years later, the cassette Walkman has been rendered an anachronism by MP3 players and iPods.

Demand for cassette players in Japan is now largely limited to elderly users.

But Sony will continue production of the cassette Walkman in China to accommodate users abroad, including in the U.S., Europe and some Asian countries, Nakamura said.