Doing Time (刑務所の中, Keimusho no Naka) is a 2002 film directed by Korean-Japanese film director Yōichi Sai. Based on Kazuichi Hanawa's manga, it follows the day-to-day routine of a middle-aged inmate at a low security Japanese prison.

The film uses a series of short vignettes to portray, often with understated humour, different aspects of prison life, especially the unvarying daily routines, the highly detailed rules, and the petty obsessions and minor pleasures that occupy the inmates' thoughts and conversations.

The film is based on the manga of the same name, which relates the author's experiences during a three-year prison sentence.