Using a transmittance adjusting device 32 decreasing a transmittance of at least from 460 nm to 500 nm, which is a wavelength range between a point of end P1end of a first optical absorption peak P1max of hemoglobin and a point of start P2start of a second optical absorption peak P2max of hemoglobin, to between 20% and 70% for illuminating light from an illuminating light supply section 6 or reflected light from an object, during observation of the inside of a body cavity, enhanced display of vessels with color reproduction that has no difference from that in observation under visible light, enabling color reproduction similar to that in observation under visible light and further enhanced display of vessels.
