An apparatus and method are provided for generating a superimposed image of a visible light image and a fluorescence image having a noise level which substantially coincides with a noise level of the visible light image. A fluorescence image noise reduction unit executes noise reduction processing on a fluorescence image and generates a noise reduced fluorescence image, an image superimposing unit generates a superimposed image of a visible light image and a noise reduced fluorescence image according to a set superimposing rate, and a fluorescence image noise reduction intensity calculation unit calculates a noise reduction intensity which is applied to the noise reduction processing on the fluorescence image. Even when the superimposing rate is changed, a noise reduction intensity is calculated having a value which makes a noise level of the noise reduced fluorescence image substantially coincide with a noise level of the visible light image forming the superimposed image.
