A supply pipe for supplying air to the peripheral surface of a circuit board container unit is provided in a test head. Nozzles are connected to the supply pipe. Each nozzle has at least one hole opposing a circuit board and corresponding to one IC on the circuit board. The circuit board has a parts mounted portion that generates a small amount of heat. The circuit board is covered with a case. A vent hole is formed on the microscope column side. A discharge pipe is connected to the vent hole and communicates with the outside of the test head. With this arrangement, each circuit board can be uniformly and efficiently cooled.