A pressure measuring device includes a housing and a rod which is movable in the axial direction in the housing under the effect of combustion chamber pressure where the rod protrudes from the housing. A sensor measure combustion chamber pressure acting on the rod, and a first diaphragm is attached to the housing through which the rod extends. A second diaphragm is attached to the housing through with the rod extends between the sensor and the first diaphragm. The second diaphragm generates a return force when the rod undergoes axial displacement caused by pressure on the rod.