A photoacoustic apparatus includes light irradiation means (100) arranged to irradiate an object with light； receiving means (400) arranged to convert a photoacoustic wave generated from the object irradiated with the light from the light irradiation means into an electric signal； optical coefficient acquiring means (720) configured to acquire optical coefficient information of the object； sound speed acquiring means (740) configured to acquire sound speed information of the object by using the optical coefficient information acquired by the optical coefficient acquiring means； and object information acquiring means (730, 750, 760, 780) configured to acquire object information by using the electric signal and the sound speed information.
