A subject is avascularized while changing the avascularization pressure between the avascularized condition and the non-avascularized condition. A receiving circuit receives a detection signal obtained by detecting a photoacoustic wave generated in the subject by emission of measurement light to the subject. Photoacoustic image generation means generates a photoacoustic image based on the detection signal of the photoacoustic wave. Motion detection means detects the motion of each of a plurality of control points set in each photoacoustic image based on photoacoustic images at a plurality of times. Region of interest setting means sets a region of interest based on the motion detected at each control point. Blood flow information generation means generates blood flow information based on the signal strength of the photoacoustic image in the region of interest.
