An atomic absorption spectrophotometer is disclosed in which, in order to detect the temperature of a graphite cuvette correctly on the basis of the radiation emitted from the inner wall of the graphite cuvette, the above radiation and the measuring light emitted from a hollow cathode lamp are both taken out by the same optical members, and then the radiation is separated from the measuring light, to be detected and used for measuring the temperature of the graphite cuvette.