An illuminance calibrating method of an illuminator having a light source (231, 241, 251) capable of changing illuminance of an illumination light according to an applied current value, the illuminance of the illumination light being commanded by a command value, the method comprising: a light-receiving intensity measuring step for taking an image of the illumination light from the illuminator by an image pickup device capable of changing an exposure time thereof to measure the intensity of the illumination light in accordance with the applied current value at a plurality of exposure times to obtain an illumination-light-intensity measurement curve representing a relationship between the applied current value and the intensity of the illumination light for each of the exposure times; a characteristic curve calculating step for calculating a characteristic curve of an intensity of the illumination light of the illuminator and the applied current value based on the result of the light-receiving intensity measuring step comprising superposing the plurality of illumination-light-intensity measurement curve; and a command-value/current-value table generating step for generating a table storing the command value and the applied current value based on the calculated characteristic curve and an illuminance control curve that represents a relationship between the command value and the illuminance commanded by the command value, wherein the illuminance control curve is a preset curve showing a desired relationship, the characteristic curve calculating step comprises: a reference characteristic curve generating step for generating a reference characteristic curve having a reference scale of the light-receiving intensity obtained in the exposure time capable of obtaining the light-receiving intensity on the entirety of the applied current value to be calibrated; a light-receiving intensity converting step for converting the scale of the light-receiving intensity obtained at each of the exposure times to superpose on the reference characteristic curve; and a pasting step for extracting and combining effective values from each of areas (S1, S2, S3,...) of the reference characteristic curve, to generate a single characteristic curve, the effective values being the values converted by the light-receiving intensity converting step and obtained at the longest exposure time for the same applied current value for each of areas (S1, S2, S3,...). a light-receiving intensity measuring step for taking an image of the illumination light from the illuminator by an image pickup device capable of changing an exposure time thereof to measure the intensity of the illumination light in accordance with the applied current value at a plurality of exposure times to obtain an illumination-light-intensity measurement curve representing a relationship between the applied current value and the intensity of the illumination light for each of the exposure times; a characteristic curve calculating step for calculating a characteristic curve of an intensity of the illumination light of the illuminator and the applied current value based on the result of the light-receiving intensity measuring step comprising superposing the plurality of illumination-light-intensity measurement curve; and a command-value/current-value table generating step for generating a table storing the command value and the applied current value based on the calculated characteristic curve and an illuminance control curve that represents a relationship between the command value and the illuminance commanded by the command value, wherein the illuminance control curve is a preset curve showing a desired relationship, the characteristic curve calculating step comprises: a reference characteristic curve generating step for generating a reference characteristic curve having a reference scale of the light-receiving intensity obtained in the exposure time capable of obtaining the light-receiving intensity on the entirety of the applied current value to be calibrated; a light-receiving intensity converting step for converting the scale of the light-receiving intensity obtained at each of the exposure times to superpose on the reference characteristic curve; and a pasting step for extracting and combining effective values from each of areas (S1, S2, S3,...) of the reference characteristic curve, to generate a single characteristic curve, the effective values being the values converted by the light-receiving intensity converting step and obtained at the longest exposure time for the same applied current value for each of areas (S1, S2, S3,...).