Abstract: A thermostatic expansion valve includes a valve housing having upper and lower passages. In the lower passage a valve member urged by a spring toward a valve seat of a valve port formed therein is provided. At the top of the housing a driving unit for driving the valve member to open and close the port is attached. The unit has a housing partitioned by a diaphragm into upper and lower pressure operating chambers. A diaphragm driving fluid is filled in the upper chamber, and the lower chamber is connected to a refrigerant circulating pipe between an evaporator pressure regulator and a compressor while the upper passage to the pipe between an evaporator and the regulator and the lower passage to the pipe between the evaporator and an condenser. In the housing a valve member driving rod extends from the diaphragm to the port and crosses the upper passage. The top end of the rod is hermetically fixed to the diaphragm and the lower end abuts the valve member against the spring.