A laser energy measuring device with which laser light radiated onto a substrate can be evaluated accurately. The laser energy measuring device includes: inside or outside an illuminating optical system, a first beam splitter which reflects laser light by any one of P-polarized reflection and S-polarized reflection; a second beam splitter which performs the other of P-polarized reflection and S-polarized reflection with respect to first reflected light reflected by the first beam splitter; a first measuring unit which measures energy of second reflected light reflected by the second beam splitter; and a second measuring unit which measures energy of transmitted light that has been transmitted through the second beam splitter.