An image processing device for an endoscope, wherein a wavelength band filter for shielding at least a part of the blue wavelength band is disposed in front of an image pickup element built into the endoscope, for image processing the signal output by said image pickup element includes means for generating color image signals whilst switching between a normal-light image mode using white light and a fluorescence image mode including fluorescence information and adjusting means for adjusting the gain of a prescribed color signal of said color image signals.