A subject information processing apparatus, comprising: a plurality of first acoustic conversion elements (002, 014), each of the plurality of first acoustic conversion elements (002, 014) being adapted to receive an acoustic wave having a first frequency that is transmitted from an acoustic wave transmitter and reflected inside a subject, and convert the acoustic wave into a first analog signal; a plurality of second acoustic conversion elements (002, 015), each of the plurality of second acoustic conversion elements (002, 015) being adapted to receive an acoustic wave having a second frequency that is generated when light emitted from a light source is irradiated to the subject, and convert the acoustic wave into a second analog signal; an A/D converter adapted to convert the first and second analog signal into a first and second digital signal at a same sampling frequency; a data memory adapted to retain the first and second digital signal converted by the A/D converter; and a processor adapted to generate image data based on the digital signal output from the data memory, wherein the first frequency is higher than the second frequency, wherein the A/D converter comprises channels corresponding to the first and second acoustic conversion elements, each of the channels being inputted the first and second analog signals, characterized in that the data memory comprises channels corresponding to the first and second acoustic conversion elements, each of the channels being inputted the first and second digital signals outputted from the A/D converter, and the data memory is adapted to output the second digital signal more sparsely than the first digital signal so that the number of samples per unit time of the second digital signal in depth direction is smaller than the number of the samples per unit time of the first digital signal in depth direction. a plurality of first acoustic conversion elements (002, 014), each of the plurality of first acoustic conversion elements (002, 014) being adapted to receive an acoustic wave having a first frequency that is transmitted from an acoustic wave transmitter and reflected inside a subject, and convert the acoustic wave into a first analog signal; a plurality of second acoustic conversion elements (002, 015), each of the plurality of second acoustic conversion elements (002, 015) being adapted to receive an acoustic wave having a second frequency that is generated when light emitted from a light source is irradiated to the subject, and convert the acoustic wave into a second analog signal; an A/D converter adapted to convert the first and second analog signal into a first and second digital signal at a same sampling frequency; a data memory adapted to retain the first and second digital signal converted by the A/D converter; and a processor adapted to generate image data based on the digital signal output from the data memory, wherein the first frequency is higher than the second frequency, wherein the A/D converter comprises channels corresponding to the first and second acoustic conversion elements, each of the channels being inputted the first and second analog signals, characterized in that the data memory comprises channels corresponding to the first and second acoustic conversion elements, each of the channels being inputted the first and second digital signals outputted from the A/D converter, and the data memory is adapted to output the second digital signal more sparsely than the first digital signal so that the number of samples per unit time of the second digital signal in depth direction is smaller than the number of the samples per unit time of the first digital signal in depth direction.