A V-LED, B-LED, G-LED and R-LED for an endoscope are all driven to apply normal light to an object of interest in a body. An image sensor images the illuminated object and outputs an RGB image signal. A measurement sensor measures a light amount of red light from the R-LED. A light source controller acquires a current value for the R-LED according to a light amount signal from the measurement sensor and a target light amount signal for the R-LED. A normal color converter and the R-LED receive a current of the current value. Each LUT_Mij in the normal color converter is referred to for outputting a matrix coefficient according to the current value of the R-LED. The RGB image signal is converted into a processed image signal by matrix operation according to the matrix coefficient.
