Abstract: In a thermostatic expansion valve having a thermo bulb, a valve opening degree is defined by the force difference between a first force at one side surface of a diaphragm and a second force at the other side surface thereof. The former force is the sum of the pressure of a refrigerant, sensed at the downstream side of a valve seat and applied on one side surface by an auxiliary pressure applying capillary tube, and the biasing force, applied on one side surface by a valve body spring. The latter force is the sum of the pressure of an actuator vapor, contained in a thermal bulb and applied on the other side surface of the diaphragm, and the pressure of the refrigerant, sensed at the upstream side of the valve seat in a refrigerant pathway of a valve housing and applied on the other side surface by way of a force transmitting member.