A breath sensor (1) includes a heat exchange portion (41) that allows heat exchange between breath discharged from a second chamber C2 and breath introduced into a first chamber C1. Therefore, breath introduced into the first chamber C1 can be heated by breath discharged from the second chamber C2, to increase the temperature of the introduced breath. Since the temperature of the breath is increased, an effect of reducing power consumption of a heater (29c) in heating a conversion portion (21) and a detection portion (29a) is realized. The heater (29c) heats both the conversion portion (21) and the detection portion (29a) to a temperature in an operation or activation temperature range. Further, power consumption for heating to an operation temperature can be reduced by preheating the introduced breath as described above.
