An aspect of the present invention is to provide a mirror surface angle adjusting device in which an assembly error between first housing (A1) and second housing (A2) does not affect the assembly accuracy of worm wheels (A71) badly, and which can be assembled by simple and prompt processes. The mirror surface angle adjusting device according to the aspect is characterized in that the worm wheels (A71) contained in the actuator (A) are held by the second housing (A2) in such a way that the worm wheels are not detached along their respective central axes and rotate around the respective central axes. This mirror surface angle adjusting device can be assembled by simple and prompt processes. In addition, even if there is any assembly error between the first housing (A1) and the second housing (A2), this error does not affects the assembly accuracy of the worm wheels (A71) badly.