A circuit to appropriately adjust the emission intensity of LEDs of various colors. By means of a first optical sensor (11), the detection range of which includes the peak wavelengths of LEDs (10R), (10G), and (10B) of multiple colors and the detectable peak wavelength of which is shorter than the shortest peak wavelength of the LEDs (10R), (10G) and (10B), and a second optical sensor 12 the detectable peak wavelength of which is longer than the longest peak wavelength of the LEDs (10R), (10G), and (10B), the LEDs (10R), (10G), and (10B) of each color are lighted one color at a time and the emission intensity is measured. When the measurement result of the first optical sensor (11) indicates an increase and the measurement result of the second optical sensor indicates a decrease, it is known that the emitted light has shifted to a shorter wavelength, and in the opposite case, that it has shifted to a longer wavelength. In the case of a change in intensity rather than a shift in the emitted wavelength, the measurement results of both first optical sensor (11) and second optical sensor (12) will be a decrease or an increase, so that a shift can be discriminated from a change in intensity, and can be detected.