PURPOSE: To extract light at a large separating angle by inclining the sticking faces of transducers so that the bearings of diffracted beams of fixed incident light beams are different in accordance with ultrasonic waves radiated from respective transducers.

CONSTITUTION: The sticking faces of the transducers are set up so that angles formed by the surfaces of excited acoustoelastic waves and an incident light beam 5 satisfy Bragg's condition and the transducers 11, 12 are stuck to an acoustooptic element. A part of the incident light is diffracted by an acoustoelastic wave 31 and diffracted light 61 and transmitted light 7 are generated. When the Bragg's angle is defined as θ, an angle formed by the transmitted light 7 and the diffracted light 61 is 2θ and an angle formed by the diffracted light 61 and diffracted light 62 can be set up to a large value 4θ, so that the diffracted light beams 61, 62 and the transmitted light 7 can be easily separated and extracted.