Rash (1971)

Jinmasin

A sixty-year old retired salaryman lives alone in a hut alongside a river. He develops a recurring rash which he discovers to be psychosomatic. One day he discovers a woman who had tried to commit suicide and she stays with him to cook. The man learns how to control the rash as well as his erection. Feeling reinvigorated, he leaves a phallic mushroom in the woman's bed at night.

(Source: Wikipedia)