Sony, pocket sized recorder, 1981. The TCS-310 did form the basis for an early budget Walkman model, the WM-1.
The prototype of the Walkman was built in 1978 by audio-division engineer Nobutoshi Kihara for Sony co-chairman Masaru Ibuka, who wanted to be able to listen to operas during his plane trips. It was marketed 1979 as the Walkman in Japan, although Akio Morita hated the name. Source