aru koroshiya aka a certain killer (kazuo mori, 1967. japan)

from moma.org:

Employed as a cook in a restaurant, a man supplements his income by working as a contract killer. When he murders a Yakuza boss, he must go into hiding in a shabby suburb. A gritty morality tale that finds its emotional core in the lost dreams of the postwar generation.

from imdb.com:

The main character is a man from the WW2 generation who has lost his dreams in post-war Japan. While working as a cook in a restaurant he also earns some money as a contract killer. He kills a Yakuza-boss using a tatami-needle and hides in a shabby apartment in a suburb.