An inclination angle adjusting mechanism includes a mounting plate to which an image pickup device is mounted; a reference member holding the mounting plate; through-holes formed in the mounting plate; screw bearing seats projecting from the reference member; adjustment screws screwed into female screw holes formed in the screw bearing seats, respectively, and head portions of the adjustment screws being in contact with the mounting plate; and a biasing device so as to bring the mounting plate into contact with back surfaces of the adjustment screws. Maximum tightening positions of the adjustment screws are defined by engagement of back surfaces of the head portions with ends of the screw bearing seats, wherein the mounting plate remains not in contact with the reference surface.