Abstract: In a method and apparatus for measuring temperature by using a state change of a working fluid, a temperature measurement is executed in a manner such that the working fluid is initially supplied at a constant mass flow rate into a flow channel having a throttle portion at a temperature-sensitive portion. Upon the measurement of a pressure difference between opposite ends of the throttle portion, the temperature can be determined through a calculation using the measured pressure difference. The temperature measuring apparatus includes a source of a working fluid and a probe. The probe includes an external cylinder closed at one of its ends and an internal cylinder which is accommodated in the external cylinder and has a capillary tube at its forward end. The apparatus further includes a supply tube for introducing the working fluid from the source into either the internal cylinder or the external cylinder, and a pressure control device.