PURPOSE: To detect and notify flow-in of outer air by calculating the pressure rising rate of a capturing room and deciding whether flow-in of outer air is present or not based on the calculated pressure rising rate.

CONSTITUTION: Upon starting operation of an absorption chiller, a microcomputer 24 reads in the signal from a pressure detector 23 in a capturing room. If the pressure is lower than 70 mm, the microcomputer 24 receives signal from the detector 23 every predetermined time until 1 hour elapses after current recording time and decides whether the pressure in the capturing room 3 is 70 mm or above and then stores the pressure in a capturing room 5 in an RAM. The microcomputer 24 calculates the pressure rising rate and decides whether a set level (3 mmHg/h) is exceeded or not. If the set level is exceeded, the microcomputer 24 operates an informing unit 25 and an exhaust pump 22 to notify that the outer air is flowing into the chiller and exhaust uncondensed gas in the chiller.