The present invention relates to a plain bearing (1) having: a bearing outer circumferential part (2) formed from a metal base material; and a resin layer (3) formed on a surface of the bearing outer circumferential part (2) serving as the sliding surface thereof. The metal base material is an unsintered compact obtained by pressure-forming a starting material powder having a metal powder capable of forming an oxide film as a main starting material, and the oxide film is formed between metal powder grains by steam treating or the like. The present invention thus makes it possible to maintain bearing properties over a long period of time while also keeping costs low.