A light source device of an endoscope system comprises a light source and a light-source controller. The light source emits in a flash-emitting mode that the light source flashes in a flash interval longer than a field period of an imaging sensor for the endoscope system and for a flash period shorter than the field period. The light-source controller controls the light source so that the light source emits in the flash-emitting mode within an imaging period that is a period excluding a reading period within the field period. The flash interval is defined as a period from when the flash of the light source commences to when the next flash of the light source commences. The flash period is defined as a period from when the flash of the light source commences to when the flash of the light source is completed.
