An adverse effect of position displacement during measurements in calculating oxygen saturation can be decreased with an apparatus having: an acoustic wave detector, for receiving acoustic waves inside a subject, and for converting the acoustic waves to signals and a processing apparatus for deriving biofunctional information using profiles of absorption coefficient derived from the signals, in which the processing apparatus includes: a first unit for deriving, from signals corresponding to light of first wavelength, first data showing a profile of first absorption coefficient, and from signals corresponding to light of second wavelength, second data showing a profile of second absorption coefficient and a second unit for deriving the biofunctional information using the first and second data, and in which the second data has lower image spatial resolution than the first data.
