PURPOSE: To unify a sample while shortening generation time, by measuring a intensity distribution from the center to the bottom of a peak selected in an emission spectrum to generate a calibration curve.

CONSTITUTION: A single reference sample 4 is made to emit light to select one peak in an emission spectrum obtained and intensity at the center thereof is measured to bring a measured value into a measurement control circuit 24. Then, it is judged whether the measured value is below an allowable value preset or not and when it is below the allowable value, detection sensitivity of a photodetector 20 is increased repeatedly until the measured value exceeds the allowable value. When the allowable value is exceeded, a wavelength scanning mechanism 22 is controlled so that the wavelength position is varied by a fixed value from the center to the foot of the selected peak to turn a diffraction grating 10 by a fixed value. Thus, intensity of photometry is changed, making it equivalent falsely to that when the density of a sample and emission intensity of a light source lamp are varied.