At the time of treating a same diseased part by both endoscope devices (1A, 1B), when a solid state image pickup element (39) of the endoscope device (1A) detects illumination light from a xenon lamp (158), which is irradiated from an illumination lens (40) of the endoscope device (1B), a system controller (156) performs control so as to reduce light quantity of the xenon lamp (158) of the endoscope device (1B) based on a level of luminance signal outputted from the solid state image pickup element (39) of the endoscope device (1A). Similarly, when a solid state image pickup element (39) of the endoscope device (1B) detects illumination light from the xenon lamp (158), which is irradiated from an illumination lens (40) of the endoscope device (1A), the system controller (156) performs control so as to reduce light quantity of the xenon lamp (158) of the endoscope device (1A).
