who invented the walk man ?

Sony Walkman WM-2 the best-selling model with plastic battery case and belt clip 1981

Walkman is a music playback device produced by Sony but now it is used to market Sony's portable audio and video players as well as a line of former Sony Ericsson mobile phones 
when Walkman introduced it changed the habits of listening to music where it allows people to carry their audio records anywhere and listen to them through lightweight headphones. 
Walkman was designed and invented by audio division engineer Nobutoshi Kihara  

Nibutoshi Kihara

Mr Nobutoshi Kihara invented the Walkman because Sony co-chairman Akio Morita wanted to listen to operas during his frequent trans-Pacific plane trips

Akio Morita

The walkman was marketed in 1979 in Japan

WalkmanTPS-L2 in 1979

Mr. Akio Morita hated the name Walkman and asked to change it but he couldn't because a promotion campaign had begun using the brand name and it would be so expensive to change.
The walkman by Sony faced hard competition from other companies such as : Panasonic , Toshiba and Aiwa  but the personalization of the gadget worked in its favor for almost 20 years and the essential design remained unchanged.