The light beam measurement apparatus comprises a beam splitter that divides a light beam emitted from a light source unit into two luminous fluxes, a semi-transmitting/reflecting surface that reflects part of one of the divided luminous fluxes back in the opposite direction to the direction of incidence as a sample luminous flux, and reflection-type reference light producing means that converts part of the luminous flux transmitted through the semi-transmitting/reflecting surface into a wavefront-shaped reference luminous flux and outputs this reference luminous flux; this light beam measurement apparatus can carry out both wavefront measurement and light beam spot characteristic measurement on a light beam simultaneously.