A subject information acquisition device having a light source for emitting light to a subject an acoustic wave detection unit configured to receive an acoustic wave generated by the subject in response to the light, and convert the received acoustic wave into an electric signal a signal processing unit configured to implement emission of the light and acquisition of the electric signal at a non-periodic sampling timing, and add together electric signals acquired in time series at each sampling timing and an image generation unit configured to generate an image representing characteristic information of the subject on the basis of the added electric signals.