PURPOSE: To prevent dew from condensing onto a printed circuit board at a low-temperature testing time by producing dry air as ambient environment for examining a printed circuit board to lower the dew point.

CONSTITUTION: At a low-temperature testing time, a force draft blower 16 and a heater 8 are operated until a printed circuit board 3 is carried into an examining device 2, and (a suction blower 17 is stopped) air having a humidity lower than that of air within a pre-cooling-heating device 1 is introduced into an examining device 2. After the printed circuit board 3 is carried in the examining device 2 and is set at a predetermined position, the operation of a heater 8 is stopped and further a suction blower 17 is operated, and a cold air is sent to the printed circuit board 3 and examined at a predetermined temperature. Since the humidity of ambient air of the printed circuit board 3 carried from the pre-cooling-heating device 1 into the examining device 2 is low and a part of cold air is sent to the circumference of the printed circuit board 3, the condensation of dew on the circuit board 3 can be prevented.