An optical device includes a first optical system having an optical element, a second optical system having a lens and disposed at a reduction side of the first optical system, a first holding member holding the optical device, a second holding member holding the lens, and a movement mechanism configured to move the first holding member in optical axis directions. The optical element has a reflection surface. The first holding member has a first holding portion holding the optical element and a first coupling portion extending from the first holding portion to a second optical system side. The movement mechanism has a transport mechanism configured to move the first coupling portion along the optical axis directions, and a guide mechanism configured to guide the first holding member in the optical axis directions. The guide mechanism restricts rotation of the first holding member around the optical axis.