To make an appropriate inclination displacement correction by grasping a present state relating to an inclination displacement correction.

A cam face 73a of a cam member 73 drives a link member 74, thereby a lens support member 70 is rotationally driven around a rotation shaft 72 while holding an optical lens 71. Having, as a starting position, the rotating position of the lens support member 70 set as a present set position as a result of the previous inclination displacement correction, a belt-like image G is formed on an intermediate transfer belt 20 in synchronization with the rotation of the cam member 73. Based on the set position of the lens support member 70, obtained by detecting time taken from the start of the formation of the belt-like image G to the formation of a blank portion S after the passage of a step portion D of the cam face 73a through the position (drive position X) of the link member 74, a cam mechanism CM is operated so that the step portion D is located in a position corresponding to a half rotation of the cam member 73 with respect to the drive position X. Then, an inclination correction is carried out.