To provide a rotation angle adjusting mechanism capable of easily and properly adjusting a rotation angle of an electric apparatus with an angle not easily changed by external stress or the like after adjustment.

As a member sandwiched between a fixed side member and an adjusted side member, a gear-like attachment is provided which is formed by overlapping the fixed side gear in which teeth are formed at every angle a° with constant intervals with the adjusted side gear in which teeth are formed at every angle b° with constant intervals with central axis identical along a rotation axis direction. At the fixed side member, a fixed side gear engagement groove is formed with which the fixed side gear can be engaged in a plurality of lanes. At the rotation axis of the adjusted side member, an adjusted side gear engagement groove is formed with which the adjusted side gear can be engaged in a plurality of lanes. The angle at which the fixed side gear is engaged with the fixed side gear engagement groove and the angle at which the adjusted side gear is engaged with the adjusted side gear engagement groove are adjusted.