A biological information processing apparatus includes the following elements. A light source irradiates biological tissue with light. A transducer functions as an ultrasonic wave transmitting unit that applies an ultrasonic wave to a local region in the biological tissue. A photodetector detects modulated light obtained by modulating the light from the light source with the ultrasonic wave in the local region. The transducer also functions as an acoustic wave detecting unit that detects an acoustic wave emitted from the local region at a time when the local region absorbs the light from the light source. An absorption characteristic in the local region is calculated using an acoustic signal, serving as an output of the acoustic wave detecting unit, on the basis of a light intensity in the local region calculated based on a modulation signal, serving as an output of the photodetector.