A spectrometer is provided with an integrating sphere 20, inside which a sample S of a measurement target is disposed and which is adapted for observing measured light emitted from the sample S, and a Dewar vessel 50 which retains a refrigerant R for cooling the sample S and at least a portion of which is located so as to face the interior of the integrating sphere 20. Gas generated from the refrigerant R is introduced through predetermined gaps G1-G6 functioning as a gas introduction path and through a plurality of communicating passages 64 formed in a support pedestal 61, into the integrating sphere 20. The gas introduced into the integrating sphere 20 absorbs water in the integrating sphere 20 to decrease the temperature in the integrating sphere 20, so as to prevent dew condensation from occurring on a portion of a second container portion 50b of the Dewar vessel 50 exposed in the integrating sphere 20. This can prevent occurrence of dew condensation even in the case where the sample S is measured in a cooled state at a desired temperature.