A spectrometer 1A is provided with an integrating sphere 20 for observing measured light emitted from a sample S of a measurement target, and a Dewar vessel 50 which retains a medium R for regulating temperature of the sample S, so as to cover the sample S and a second container portion 50b of which is located so as to face the interior of the integrating sphere 20. The sample S can be easily regulated at a desired temperature with the use of the Dewar vessel 50 retaining the medium R so as to cover the sample S. As the second container portion 50b is located so as to face the interior of the integrating sphere 20, the temperature of the sample S is regulated by the medium R, while inhibiting an external ambience around the integrating sphere from affecting the sample S. Therefore, the sample S can be efficiently regulated at a desired temperature.