A method of manufacturing an optical interferometer includes a first step of forming a first semiconductor portion for a beam splitter and a second semiconductor portion for a movable mirror on a main surface of a support substrate and a first insulating layer formed on the main surface, a second step of disposing a first wall portion between a first side surface of the first semiconductor portion and a second side surface in the second semiconductor portion, and a third step of forming a mirror surface in the second semiconductor portion by forming a first metal film on the second side surface using a shadow mask. In the third step, the first side surface is masked by the mask portion and the first wall portion and the first metal film is formed in a state in which the second side portion is exposed from an opening portion.