A position of a light absorber existing in a subject and an initial sound pressure of an acoustic wave generated at the light absorber are calculated from an electric signal converted from the received acoustic wave generated in response to irradiation of the subject with light. An optical absorption coefficient and an optical scattering coefficient of the subject are calculated using the position of the light absorber and the initial sound pressure of the acoustic wave generated at the position of the light absorber. A light quantity distribution in the subject is calculated using the optical absorption coefficient and the optical scattering coefficient of the subject. An optical absorption coefficient distribution in the subject is calculated using the light quantity distribution in the subject and an initial sound pressure distribution in the subject obtained from the electric signal.
