PURPOSE: To make possible measurement of integral value of an absorbance peak by separating a background absorption peak and a scattering peak, by integrating only the absorbance from starting time to finishing time of the real absorbance.

CONSTITUTION: A line spectrum of an element to be measured is discharged from a hollow cathode lamp and its energy is absorbed by a resonance line of a sample in a high temperature atomizing part and the line spectrum other than the resonance line is passed through as it is. Further, only the light near the resonance line from a spectroscope is made incident to a detector and only the magnitude of the resonance line decreased by the absorption of the element in the sample is detected. An output of this detector is added to a high speed peak-shaped reader consisting of a computer and an A/D converter and the value of absorbance of atomizing time at every time is read and then, is stored in a memory. Then, the integral value of an absorbance peak is found separating from the absorbance peak of absorption and scattering of molecules by integrating only the absorbance from starting to finishing time of the real value of the atomic absorbance.