PROBLEM TO BE SOLVED: To reduce variation of a color temperature of output light between plural illumination devices.SOLUTION: The method according to the present invention includes: a measurement step of measuring color coordinates of respective output light when plural light sources with different color temperatures are lit at a first output ratio, and when they are lit at a second output ratio in which the output ratios of the plural light sources are different from those of the first output ratio; a calculation step of calculating a color coordinate of an intersection of a straight line passing through coordinates at two points measured in the measurement step and a color temperature straight line of a predetermined color temperature, and a ratio of brightness of each light source in the color coordinate at the intersection; and an adjustment step of adjusting a ratio of an output of each light source so that it becomes a ratio of brightness of each light source at the color coordinate at the intersection
