A light beam measurement device is provided with: a polarimeter which includes a first measurement unit beam splitter which is placed upon an optical path of laser light, and which measures the polarization state of partially reflected laser light in the first measurement unit beam splitter; a beam profile meter which includes a second measurement unit beam splitter which is placed upon the optical path of the laser light, and which measures the beam profile of the partially reflected laser light in the second measurement unit beam splitter; and a laser beam travel direction stability meter which measures stability of the laser beam travel direction for the laser light. The first measurement unit beam splitter and the second measurement unit beam splitter may be formed of material including CaF2.
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