An IC tester which is capable of reducing the time required before completion of testing on all of ICs to be tested is provided. The depth (length in the Y-axis direction) of the constant temperature chamber 4 and the exit chamber 5 is expanded by a dimension corresponding approximately to one transverse width (length of the minor edge) of the rectangular test tray 3, and two generally parallel test tray transport paths or alternatively a widened test tray transport path broad enough to transport two test trays simultaneously with the two test trays juxtaposed in a direction transverse to the widened test tray transport path are provided in the section of test tray transport path extending from the soak chamber 41 in the constant temperature chamber 4 through the testing section 42 in the constant temperature chamber 4 to the exit chamber 5 so that two test trays may be simultaneously transported along the two test tray transport paths or the widened test tray transport path.