PURPOSE: To perform high temp./low temp. cycle tests automatically under programmed control and to improve the efficiency of the testing operations by setting the environmental conditions for testing the temp. of printed board units in a control section.

CONSTITUTION: A function tester 1 for testing the functions of a printed board unit 23 wherein electronic parts, etc. are packaged on a printed board is provided with a thermal box 7 for covering the unit 23, a heat chamber 4 having a duct 4a for feeding of hot wind into the box 7, a cold chamber 5 having ducts 5aW5c for circulating cold wind in the box 7, and a control section 8 for controlling the chambers 4 and 5 selectively. The temp. of atmosphere in the box 7 is controlled to a required temp. by the selection of the chambers 4 and 5, whereby the unit 23 is tested.