A light source that emits beam light, a beam shaping unit that shapes the beam light, and a pulse control unit that forms the beam light into pulse light are included. The light source emits beam light that has a wavelength that is to be absorbed by a measurement-target substance. The pulse control unit forms beam light that is emitted from the light source and with which a measurement-target part is irradiated, into pulse light that has a preset frequency and has a pulse width that is a reciprocal of twice the frequency. The beam shaping unit shapes the beam light so that a beam radius of the beam light that is emitted from the light source and with which the measurement-target part is to be irradiated is equal to a value obtained by dividing a speed of sound by π×f, where f denotes the frequency.