A galvano motor 10 includes a motor shaft 1, a coil 5 which rotationally drives the motor shaft 1, and an encoder scale 6 which is joined to one end of the rotating shaft, the motor shaft 1 is configured so that a mirror 9 which is heavier than the encoder scale 6 at the other end opposite to the one end to which the encoder scale 6 is joined, a phase crossover frequency fphase in open-loop characteristics of the galvano motor 10, a torsion resonance frequency fscale between a center part of the motor shaft 1 and the encoder scale 6, and a torsion resonance frequency fmirror between the center part of the motor shaft 1 and the mirror 9 satisfy the relation of fphase