A photoacoustic wave induced in a subject to be examined by illumination of the subject to be examined with light is detected. A first photoacoustic image corresponding to a frequency component less than or equal to a predetermined frequency and a second photoacoustic image corresponding to a frequency component higher than a predetermined frequency are generated based on a detection signal of the detected photoacoustic wave. The first photoacoustic image and the second photoacoustic image are combined together by placing, on a pixel in the first photoacoustic image the pixel value of which is less than or equal to a threshold, a pixel in the second photoacoustic image corresponding to the pixel in the first photoacoustic image.
