PROBLEM TO BE SOLVED: To acquire the same contrast of blood vessels in observation images by endoscopes with different light transmission properties of light guides.SOLUTION: A plurality of endoscopes with different light transmission properties of light guides are exchangeably connected to a connection part. A semiconductor light source emits light for blood vessel information observation. A light source control part executes control to increase output of the semiconductor light source so as to compensate for decrease in an amount of emission of the light for blood vessel information observation that decreases when an endoscope with relatively low light transmissivity is connected as compared with a case where an endoscope with high light transmissivity is connected. When the output of the semiconductor light source reaches the upper limit, an image processing part performs contrast emphasis processing for an image signal output by the endoscope with relatively low light transmissivity for the light for blood vessel information observation, in addition to the image processing for an image signal output by the endoscope with high light transmissivity.
