An optical scanning device includes a correction mechanism that rotates a synchronization detection mirror around a sub-scanning axis in accordance with a change in the temperature of a casing, wherein the correction mechanism includes a fixing support part provided to the casing and fixing the synchronization detection mirror thereto, and a first adhesive part and a second adhesive part respectively provided at one end side and the other end side of the synchronization detection mirror in a width direction perpendicular to a sub-scanning direction and serving as adhesives for allowing the synchronization detection mirror to adhere to the fixing support part. The correction mechanism is configured to rotate the synchronization detection mirror around the sub-scanning axis due to a difference between of thermal deformation amounts of the first adhesive part and the second adhesive part in a thickness direction when the temperature inside the casing has changed.