Light reduction mechanism, output data correction method, and laser beam measurement device

A light reduction mechanism reducing a laser beam irradiated from a laser beam irradiation optical unit for laser processing by irradiating the laser beam to form a spot on a workpiece to be processed, the light reduction mechanism comprising:

• a first beam splitter and a second beam splitter which are a plate-type, wherein
• in a case where an X axis and a Y axis are arbitrary orthogonal coordinate axes in a plane perpendicular to an optical axis of the laser beam irradiation optical unit whose origin is in the optical axis, the first beam splitter is arranged with the X axis as a rotation axis and inclined at an angle α in a range of 30° or more and 60° or less with respect to a plane perpendicular to the optical axis, and the second beam splitter is arranged with an X′ axis, which is parallel to the X axis and passes through the optical axis, as a rotation axis, and inclined at an angle -a with respect to a plane perpendicular to the optical axis.