PURPOSE: To provide an optical shutter suitable for the miniaturization of optical system and the reduction of the manufacturing cost of product and also excellent in preventing the contamination in the optical system or a measuring environment without causing a large impact noise when it is operated.

CONSTITUTION: The optical shutter 55 is prepared for selecting and setting a light shielding state where the light made incident on an optical path is shielded, or a light transmissible state where the light made incident on the optical path is transmitted as it is, by moving a light shielding plate 13 into/out of the optical path of the optical system, and the light shielding plate 13 is mounted on the movable piece 11f of an electromagnetic relay 11 for switching a connecting contact by the magnetization of a coil 11h installed at the inside, and the light shielding plate 13 is moved into/out of the optical path by moving the movable piece 11f at the time of switching the connecting contact for the electromagnetic relay 11.