PURPOSE: To obtain a phase-shift-reticle-performance inspection apparatus wherein a mechanical constitution is not required, the deviation of an optical path length from an initially set value (an ideal optical path length) can be corrected sequentially with high accuracy and a high-accuracy inspection can be performed always stably.

CONSTITUTION: A filter 7, for optical-path-length correction, which is composed of a flat-boardlike glass plate is inserted between a beam splitter 2a which separates a laser beam radiated from a laser unit 1 into two luminous fluxes and a reflector 8a which reflects the luminous flux which has not been passed through the inside of the beam splitter 2a out of the two luminous fluxes separated by the beam splitter 2a. In addition, optical-path-length control means (a heating means 10 and a control device 11) which expand or contract, by a required amount, the filter 7 for optical-path-length correction on the basis of the phase difference, of the two luminous fluxes, obtained by a laser interferometer 9 are installed.