When an external trigger is received as a predetermined signal after receiving a signal concerning a start of imaging, controls are carried out to stop driving of a CCD type solid-state image sensor (CCD) from receipt of the signal concerning a start of imaging until receipt of the external trigger, and to start the driving of the CCD synchronously with the receipt of the external trigger. Thus, the driving of the CCD is not started immediately upon receipt of the signal concerning a start of imaging, and the driving time of the CCD can be shortened by the time from receipt of the signal concerning a start of imaging until receipt of the external trigger, thereby suppressing heat generation of the CCD.