An inter-image calculation portion includes a switch circuit made up of three switch portions for switching each of three image data (R, G, B) from a 3-board processing portion, a first divider, a second divider, a first adder, a second adder, a first LUT, a second LUT, a first clip portion, and a second clip portion. The inter-image calculation portion executes addition processing of two different fluorescent images with two different wavelength bands and division processing the two different fluorescent images with two different wavelength bands and then it executes addition processing which adds the addition results and the division results of the two different fluorescent images with two different wavelength bands or it executes subtraction processing which subtracts the addition results from the division results of the two different fluorescent images with two different wavelength bands.
