A photoacoustic apparatus includes a light source configured to generate a plurality of light beams having wavelengths different from each other, a conversion element configured to receive a photoacoustic wave that is generated in a subject in response to being illuminated with the respective light beams having wavelengths different from each other and output a signal for each wavelength, an information acquisition unit configured to acquire information in terms of a concentration of a substance existing in the subject by using the signal for each wavelength, and a specifying unit configured to specify a coefficient and instruct the information acquisition unit to use the specified coefficient in acquiring the information in terms of the concentration, wherein the specifying unit specifies, as the coefficient, a value representable by a formula including an amount of light having each wavelength, and wherein the information acquisition unit acquires information in terms of the concentration by using the coefficient specified by the specifying unit and the signal for each wavelength.