A photoacoustic apparatus of the present invention obtains distribution information of concentration of a substance inside an object using electric signals originated from acoustic waves generated from the object irradiated with a plurality of lights having a plurality of wavelengths, and includes a signal processor for obtaining a plurality of sound pressure distribution information, obtains concentration information of the substance at a certain position based on an user input, and obtains distribution information of the concentration of the substance inside the object using the sound pressure distribution information, concentration information of the substance, and information on absorption of each of the lights having the plurality of wavelengths by the substance.