A subject information accumulating apparatus comprising: first and second compression plates configured to compress a subject; an irradiation unit configured to irradiate the subject with irradiation light via the second compression plate ; an acoustic wave detector positioned opposite the irradiation unit, the detector configured to receive acoustic waves via the first compression plate , the acoustic waves being generated within the subject irradiated with the irradiation light, and to output an electric signal; an image signal generator configured to generate a signal for forming an acoustic wave image on the basis of the electric signal output from the acoustic wave detector; a photoacoustic-wave-receiving-side pressure distribution calculator configured to obtain pressure distribution information within a subject contact plane on the first compression plate ; a light-transmitting-side pressure distribution calculator configured to obtain pressure distribution information within a subject contact plane on the second compression plate ; a pressure information accumulating unit configured to obtain pressure distribution information from the photoacoustic-wave-receiving-side pressure distribution calculator and the light-transmitting-side pressure distribution calculator ; and a controller configured to display the acoustic wave image and a pressure distribution image on a display unit , and to select a display image format, wherein the pressure information accumulating unit is configured to calculate the pressure distribution image data based on the obtained pressure distribution information and in accordance with the display image format selected by the controller , said display image format being the same as that of the acoustic wave image. first and second compression plates configured to compress a subject; an irradiation unit configured to irradiate the subject with irradiation light via the second compression plate ; an acoustic wave detector positioned opposite the irradiation unit, the detector configured to receive acoustic waves via the first compression plate , the acoustic waves being generated within the subject irradiated with the irradiation light, and to output an electric signal; an image signal generator configured to generate a signal for forming an acoustic wave image on the basis of the electric signal output from the acoustic wave detector; a photoacoustic-wave-receiving-side pressure distribution calculator configured to obtain pressure distribution information within a subject contact plane on the first compression plate ; a light-transmitting-side pressure distribution calculator configured to obtain pressure distribution information within a subject contact plane on the second compression plate ; a pressure information accumulating unit configured to obtain pressure distribution information from the photoacoustic-wave-receiving-side pressure distribution calculator and the light-transmitting-side pressure distribution calculator ; and a controller configured to display the acoustic wave image and a pressure distribution image on a display unit , and to select a display image format, wherein the pressure information accumulating unit is configured to calculate the pressure distribution image data based on the obtained pressure distribution information and in accordance with the display image format selected by the controller , said display image format being the same as that of the acoustic wave image. <EOS>