To provide an optical system capable of preventing an improper image from being observed through a focal distance variable optical system.

This optical system includes the optical system 300B including an optical element 310 capable of changing a focal distance in response to a voltage, and moving means 504 for moving one part 314 of the optical system 300B when electric power supply is stopped, so as to approach a position of an image-focusing face by the optical system 300B when stopping the voltage supply to the optical system 300B (310), with respect to a position of an image-focusing face by the optical system 300B when supplying the voltage to the optical system 300B (310).