Keiji Sada returns from the War to his wife, Hideko Takamine and their son. He becomes a road worker, and she a housekeeper for the local supervisor and staff. He works hard, and drinks too much shochu, cheap liquor distilled from rice, sweet potatoes, barley, buckwheat, sugar... Japanese moonshine. Their son does well enough to go to college, but the little money they send him isn't enough.
The Shomin-Geki (in proper Japanese, it's 'shoshimin-eiga') is a Japanese performing-arts genre that focuses on ordinary people. Naruse directed them, and so did Ozu. The writer-director of this movie, Keisuke Kinoshita, worked in it frequently, and you can't get people more ordinary than these poor, hard-working two, surrounded by friends and co-workers living equally tough lives, hoping desperately for their son to do better than they did, giving up their occasional drink, even tea, doing without.
The two leads are extraordinary actors; Miss Takamine was one of the leading stars of the Japanese cinema for many years, and Sada's career, although much shorter, is distinguished by many roles in the movies of Kinoshita, Kobayashi, and even Ozu. They bring an immense dignity to these characters, even when Miss Takamine slaps her son or Sada is drunk. Perhaps it would be better to say that this movie gave them the chance to show the ferocious good character of the working poor.