PURPOSE: To facilitate measuring work and to simplify a structure while making it possible to hold measuring accuracy stably for a long period of time, by performing the measurement of pressure by detecting the displacement of a pressure receiving diaphragm by an ultrasonic wave.

CONSTITUTION: A pressure receiving diaphragm 3 is received in the housing of a sensor 1 and, for example, atmosphere pressure is applied to the filling liquid 4 in one side as reference pressure by a pressure receiving part 6 while pressure measured by mounting a pressure receiving part 7 to an object 6 to be measured 8 is applied to filling liquid 5 in the other side and the diaphragm 3 displaces corresponding to measuring pressure. Therefore the delay time of the ultrasonic wave, which was transmitted from a transmitting transducer 9 and reflected by the diaphragm 3, before received by a receiving transducer 10 changes corresponding to the measured pressure of the object 8 to be measured and, after the receiving signal of the transducer 10 is amplified by an amplifier 11, the amplified signal is applied to the transducer 9 to form a position feedback to generate oscillation which is, in turn, counted by a frequency counter 12 to obtain a count value corresponding to measured pressure.