A tomographic image generating apparatus, comprising: a laser light source unit adapted to output a laser beam to be irradiated onto a subject; an ultrasonic wave transmitting section adapted to transmit ultrasonic waves toward the subject; an acoustic signal detecting section adapted to detect photoacoustic signals generated within the subject due to irradiation of the laser beam onto the subject and to detect reflected acoustic signals of the ultrasonic waves transmitted into the subject; a trigger control section adapted to output light trigger signals that command laser beam output to the laser light source unit and to output ultrasonic wave trigger signals that command transmission of ultrasonic waves to the ultrasonic wave transmitting section; sampling means adapted to sample the photoacoustic signals and the reflected acoustic signals and to store the sampled photoacoustic signals and the sampled reflected acoustic signals in a common memory as a series of data; sampling control means adapted to output sampling trigger signals that command sampling initiation to the sampling means; photoacoustic image generating means adapted to generate photoacoustic images based on photoacoustic signals stored in the memory; and ultrasound image generating means adapted to generate ultrasound images based on reflected acoustic signals stored in the memory; the trigger control section is adapted to output one of a light trigger signal and a ultrasonic wave trigger signal, then outputting the other of a light trigger signal and a ultrasonic wave trigger signal in a state during which the sampling means is continuing sampling; and the sampling means is adapted to continuously sample the photoacoustic signals and the reflected acoustic signals without interrupting a sampling operation. a laser light source unit adapted to output a laser beam to be irradiated onto a subject; an ultrasonic wave transmitting section adapted to transmit ultrasonic waves toward the subject; an acoustic signal detecting section adapted to detect photoacoustic signals generated within the subject due to irradiation of the laser beam onto the subject and to detect reflected acoustic signals of the ultrasonic waves transmitted into the subject; a trigger control section adapted to output light trigger signals that command laser beam output to the laser light source unit and to output ultrasonic wave trigger signals that command transmission of ultrasonic waves to the ultrasonic wave transmitting section; sampling means adapted to sample the photoacoustic signals and the reflected acoustic signals and to store the sampled photoacoustic signals and the sampled reflected acoustic signals in a common memory as a series of data; sampling control means adapted to output sampling trigger signals that command sampling initiation to the sampling means; photoacoustic image generating means adapted to generate photoacoustic images based on photoacoustic signals stored in the memory; and ultrasound image generating means adapted to generate ultrasound images based on reflected acoustic signals stored in the memory; the trigger control section is adapted to output one of a light trigger signal and a ultrasonic wave trigger signal, then outputting the other of a light trigger signal and a ultrasonic wave trigger signal in a state during which the sampling means is continuing sampling; and the sampling means is adapted to continuously sample the photoacoustic signals and the reflected acoustic signals without interrupting a sampling operation.