To prevent the deterioration of the optical characteristic of a mirror and to keep the performance of an optical deflector during operation.

A strain (dynamic bending) of a reflection face of a micro mirror, particularly when operating at a high speed, is constantly observed or detected, further the result is fed back to a driving system, the dynamic bending of the reflection face is controlled, the deterioration of the optical characteristic of the mirror is prevented and the performance of the optical deflector is kept during operation. Further, an allowable area for a strain gauge can be small depending on the figure of a torsion beam and the strain gauge is not formed in the case where the strain gauge is provided on the torsion beam. Even in such a case, the vibrational state of the micro mirror is calibrated without using an external detector.