PURPOSE: To make a focus adjustment without mechanical driving by using a lens made of electromagnetic optical material as an optical system forming an image of light from an object on an image formation surface, and varying the refractive index of the lens by an electric or magnetic field.

CONSTITUTION: The lens 10 is made of the material having large electrooptic effect and transparent electrodes 11A and 11B are stuck to its surfaces. An ultrasonic wave is emitted from the transmitter and receiver 21 of a distance measurement part 20 to the object A and its reflected wave is received to calculate the distance by a measuring circuit. A control part 13 generates a specific voltage at a power source 12 according to its distance signal and applies the voltage to the electrodes 11A and 11B to vary the refractive index of the lens 10, making the automatic focus adjustment without moving the lens 10.