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 element, and a first movement mechanism configured to move the first holding member in optical axis directions along an optical axis of the optical element. The optical element has a reflection surface. The first movement mechanism has a fixing member supporting the first holding member rotatably around a rotation axis and a transport portion configured to move the first holding member along the optical axis directions according to rotation of the first holding member. The reflection surface has a shape rotationally symmetrical with respect to the rotation axis. The rotation axis and the optical axis are the same axis.