An optical device that includes a light modulation device, a projection optical device, and a retention member that holds the light modulation device and the projection optical device. The retention member includes: a projection optical device attachment section for attach the projection optical device; and a light modulation device attachment section that is provided for attachment of the light modulation device with a protrusion to a side opposite to the projection optical device along an optical-axis direction of the projection optical device, and the projection optical device attachment section includes: a fixing section that fixes the projection optical device substantially at a position of the center of gravity; a support section that is disposed opposing the fixing section in the optical-axis direction, and supports the light modulation device attachment section; and a connection section that connects together the fixing section and the support section.