A calibration method for an endoscope system having semiconductor light sources for emitting different types of illumination light with different wavelength ranges, a light source controller for controlling the semiconductor light sources with respective light source control signals, and a brightness command signal generator for generating a brightness command signal n for commanding the light source controller to change a light amount of each illumination light type based on a brightness step n (n being an integer from 0 to N-1) of N (N being an integer greater than or equal to 2) levels, a light amount ratio between the light amounts of the illumination light types being set in advance as a set light amount ratio, the calibration method being characterized by the steps of: (a) applying a first light source control signal to each semiconductor light source and allowing each semiconductor light source to emit the illumination light type to a reference object, and calculating a light amount of the illumination light type reflected from the reference object with a light amount calculator; (b) generating calibration data by associating the first light source control signals with the light amounts of the illumination light types calculated by the light amount calculator in a case where the first light source control signals are applied; (c) setting a maximum light amount of each illumination light type in accordance with the set light amount ratio and based on the calibration data; (d) setting an nth light amount for each illumination light type based on the maximum light amount for each illumination light type, the nth light amount increasing or decreasing linearly relative to the brightness step n; (e) referring to the calibration data and determining a light source control signal corresponding to the nth light amount from the first light source control signals, the determined light source control signal being set as a second light source control signal corresponding to the brightness step n; and (f) associating the second light source control signal with a brightness control signal n for the brightness step n, and generating a light control table (32a-36a, 33b, 35b, 36b, 33c-36c, 36d, 37d). (a) applying a first light source control signal to each semiconductor light source and allowing each semiconductor light source to emit the illumination light type to a reference object, and calculating a light amount of the illumination light type reflected from the reference object with a light amount calculator; (b) generating calibration data by associating the first light source control signals with the light amounts of the illumination light types calculated by the light amount calculator in a case where the first light source control signals are applied; (c) setting a maximum light amount of each illumination light type in accordance with the set light amount ratio and based on the calibration data; (d) setting an nth light amount for each illumination light type based on the maximum light amount for each illumination light type, the nth light amount increasing or decreasing linearly relative to the brightness step n; (e) referring to the calibration data and determining a light source control signal corresponding to the nth light amount from the first light source control signals, the determined light source control signal being set as a second light source control signal corresponding to the brightness step n; and (f) associating the second light source control signal with a brightness control signal n for the brightness step n, and generating a light control table (32a-36a, 33b, 35b, 36b, 33c-36c, 36d, 37d).