A position change measuring device which measures a change in position of a target object and includes a base member, a press member which is movable following a change in position of the target object, an elastic member which produces heat when contracting or absorbs heat when expanding, a heat flux sensor which outputs a signal as a function of a rate of heat flux transferred inside or outside the elastic member, and a diaphragm unit which is made of elastically deformable material. The diaphragm unit is retained by the base member in contact with the press member and works to produce force of resilience to recover the elastic member to its initial state when the elastic member contracts or expands in response to movement of the press member. This structure improves a response rate for sensing a change in position of the target object with high accuracy.