A mirror drive device in which the speed of forward and backward movement of a mirror is increased while reducing a power amount required therefor without affecting a finder image and a focus distance of an image viewed through a finder. A mirror-down cam is cam-engaged with a drive shaft provided in a mirror holder, and causes the mirror holder to enter a finder observation position of a photographing optical path. A mirror-up cam is cam-engaged with the drive shaft, and causes the mirror holder to retract from the photographing optical path. A down spring urges the mirror holder toward the finder observation position with low necessary and sufficient pressure. A motor transmits rotation to the mirror-down cam and the mirror-up cam via a shift gear train. The rotation axes of the mirror-down cam and the mirror-up cam are arranged in positions different from each other.