PURPOSE: To generate a multipulse laser by separating one pulse laser in two directions by a polarization beam splitter, introducing only one laser into a fiber, delaying it, again introducing it into the splitter, and repeating it.

CONSTITUTION: A laser beam PS1 incident to a polarization beam splitter 4 is separated into a transmitted light P1 and a reflected light S1. The light S1 is guided into a fiber 6 to become a polarized laser PS2, again introduced into the splitter 4, separated into a reflected light S2 and a transmitted light P2, and the light P2 is introduced into the fiber to form a loop. With such a configuration, if a laser light PS1 is assumed to be an incident light PIN, an emitting light POUT has a predetermined pulse delay time to be decided according to the length of the fiber 6, and a multipulse train in which an output is sequentially lowered each time the beam is circulated in the loop, is obtained. Thus, the one pulse laser can be converted into a multipulse laser.