Abstract: A region selecting means sequentially selects a plurality of partial regions, into which a range to be imaged of a subject is divided. A light irradiation detecting section detects light which is irradiated onto the subject from a laser light source. A signal obtaining section samples acoustic signals detected by probe elements corresponding to the selected partial region, and stores the acoustic signals in an element data memory. An image constructing section constructs a tomographic image of the subject based on the data read out from the element data memory. A synchronization correction processing section obtains the differences in the timings at which the light irradiation detecting section has detected irradiation of light, and corrects the temporal axes of the sampled data in the element data memory based on the obtained timing differences.