PURPOSE: To sufficiently miniaturize the device and to facilitate the assembly by eliminating an unnecessary space between respective components and providing reference surfaces.

CONSTITUTION: The optical scanning device consists of a housing 21 which supports a bearing 22, a scanner motor 23 provided with a rotor 23a formed by supporting a rotary shaft 23b rotatably in the bearing, a right-angled prism 27 fixed on the rotor 23a of the motor 23, a cover member 28 which is so provided on a housing 21 as to cover the scanner motor 23, a semiconductor laser oscillator 29 fitted to the cover member 28, a reflecting mirror 33, and a meniscus lens 34. The lower outer peripheral surface of the cylinder part 21a of the housing 21 is regarded as a plane-directional reference surface X1 for the fitting of the device to the outside and the lowermost surface of the flat plate part of the housing is used as a height-directional reference surface X2 for the fitting of the device to the outside.