A solid-state image sensor, comprising: a plurality of pixels arranged in a two-dimensional array, each pixel including a photoelectric conversion element for receiving light and producing photocharges, a transfer element for transferring the photocharges produced by the photoelectric conversion element to a detection node, and a buffer element for sending an output signal corresponding to a charge from the detection node to a pixel output line which is independently provided for each pixel; a plurality of memory sections provided for each pixel in order to hold, for each pixel, corresponding output signals extracted from a corresponding pixel through a corresponding pixel output line; a drive control means for operating the pixels and the memory sections so that, in a middle of an imaging operation where an operation of storing photocharges for one frame of an imaging action, in the corresponding detection node at each pixel and an operation of transferring output signals from each pixel through the corresponding pixel output line to a corresponding one of the memory sections provided for a corresponding pixel are repeatedly performed simultaneously at all the pixels while, for each pixel, the corresponding one memory section provided for the corresponding pixel to hold the corresponding transferred output signal is sequentially selected from the plurality of memory sections for each frame of the imaging action, the output signals corresponding to a portion or all of the pixels and belonging to two frames of the imaging action obtained at different points in time and held in the corresponding memory sections provided for a corresponding pixel are sequentially read from the memory sections concerned; and a trigger signal generating means adapted to detect a change in or movement of an imaging object on the basis of the signals corresponding to a portion or all of the pixels and belonging to the two frames which have been sequentially read under the control of the drive control means, and to generate a trigger signal based on the detected change or movement. a plurality of pixels arranged in a two-dimensional array, each pixel including a photoelectric conversion element for receiving light and producing photocharges, a transfer element for transferring the photocharges produced by the photoelectric conversion element to a detection node, and a buffer element for sending an output signal corresponding to a charge from the detection node to a pixel output line which is independently provided for each pixel; a plurality of memory sections provided for each pixel in order to hold, for each pixel, corresponding output signals extracted from a corresponding pixel through a corresponding pixel output line; a drive control means for operating the pixels and the memory sections so that, in a middle of an imaging operation where an operation of storing photocharges for one frame of an imaging action, in the corresponding detection node at each pixel and an operation of transferring output signals from each pixel through the corresponding pixel output line to a corresponding one of the memory sections provided for a corresponding pixel are repeatedly performed simultaneously at all the pixels while, for each pixel, the corresponding one memory section provided for the corresponding pixel to hold the corresponding transferred output signal is sequentially selected from the plurality of memory sections for each frame of the imaging action, the output signals corresponding to a portion or all of the pixels and belonging to two frames of the imaging action obtained at different points in time and held in the corresponding memory sections provided for a corresponding pixel are sequentially read from the memory sections concerned; and a trigger signal generating means adapted to detect a change in or movement of an imaging object on the basis of the signals corresponding to a portion or all of the pixels and belonging to the two frames which have been sequentially read under the control of the drive control means, and to generate a trigger signal based on the detected change or movement.