PURPOSE: To provide a splitter for easily dividing a high output energy without adopting any complicate optical path or high sensitive element.

CONSTITUTION: This device is constituted of a prism segmenter 26 forming plural divided light beams 28a-28c from a single light beam 16 constituted of a peripheral part and a central part. The prism segmenter 26 is constituted of plural prisms 50 which are respectively provided with an input face, output face 54, and slope 56, and the plural prisms 50 are arranged so that a central path can be formed around a central axis. The input face of the prism 50 is present in a face in the same direction substantially vertical to the central axis, and the slope 56 of the prism 50 is directed to the central axis side. When the peripheral part of the single light beam 16 is brought into contact with the input face of the prim 50 and the central part is allowed to pass through the central path, the plural divided light beams 28a-28c are formed.