A light measurement device that maintains high measurement precision. The light measurement device includes: light source that irradiates light upon measurement object; branch part that splits transmitted light or reflected light from measurement object; phase-changing unit that changes the phase of one beam of the branched light beams; phase-fixing unit that maintains the phase of the other beam of the branched light beams; adjustment mechanism, which is provided in phase-changing unit or phase-fixing unit, for adjusting the propagation direction of light; multiplexer that causes the light emitted by each of phase-changing unit and phase-fixing unit to interfere with each other; detection unit that detects light that is interfered with by multiplexer; and control unit that controls the adjustment mechanism on the basis of the luminance values of an interference image that is detected by detection unit and adjusts the propagation direction of light in phase-changing unit or phase-fixing unit.