Violet narrowband light Vn and green narrowband light Gn produced by a light source device are supplied to a complementary color type endoscope, and simultaneously applied to an observation object. In a complementary color type imaging device, first mixed pixels and second mixed pixels, which sense both of the violet narrowband light Vn and the green narrowband light Gn, are read out. The light amount ratio Z of the violet narrowband light Vn to the green narrowband light Gn is set in such a range as to make the light amount of the violet narrowband light Vn larger than the light amount of the green narrowband light Gn, and make a signal value of the second mixed pixel higher than a signal value of the first mixed pixel.
