A biological information processing apparatus includes: a light source 11 that irradiates light 12 to a light irradiation region 13A on a test object 13 an acoustic wave detector 17 that detects an acoustic wave 16 generated by a light absorber 15 in the test object upon its absorption of the light, and outputs a detection signal and an electronic control system 18 having an amplifier that amplifies the detection signal outputted from the acoustic wave detector 17. The electronic control system controls a gain of the amplifier in such a manner that a gain for a detection signal of an acoustic wave generated at a first location in the test object becomes larger as compared with a gain for a detection signal of an acoustic wave generated at a second location which exists nearer to the light irradiation region than the first location does.
