An optical device includes: a housing; and a reflection member disposed at a predetermined position within the housing, the housing includes a receiving opening through which the reflection member is inserted to be accommodated in the housing, and an attachment unit to which the reflection member is attached, the reflection member includes a front portion which has a reflection area for reflecting supplied light, a back portion positioned on the side opposite to the front portion, and a fixing unit positioned within the surface of the back portion and fixed to the attachment unit, and the fixing unit has an opening into which a position control jig inserted in an attachment direction of attaching the reflection member to the attachment unit through the receiving opening is inserted.