PURPOSE: To prevent wrong operation of alarm by providing a timer means operating a humidity sensor when the sensor detected prescribed upper limit value or lower limit value and operating an alarm means when these humidity values continued for a prescribed time.

CONSTITUTION: The objective chamber for conditioning temperature and humidity is equipped with a time measuring circuit 21C for operating an alarm means when a humidity sensor 14 installed in the chamber continuously detected a set value, e.g. ≥90% or <10% for previously set time (e.g. 1 minute). Thereby, wrong operation giving an alarm based on abnormality of humidity which humidity sensor kept in unstable state measured is prevent ed.