To provide a differential pressure sensor of noncontact type capable of maintaining high detection accuracy.

The differential pressure sensor 1 for detecting the differential pressure of the working fluid between the high-pressure side and the low-pressure side comprises: a pair of pressure chambers 2 and 3 communicating with the fluid of the high-pressure side and the low-pressure side, respectively; a plunger 4 displacing, corresponding to the differential fluid pressure activating to each pressure chamber 2 and 3; a spring 13 for energizing the plunger 4 in the axial direction; a magnetic body 11 interlocking with the motion of the plunger 4; and a Hall element 15 for detecting the amount of movement in the magnetic body 11, as the amount of variation in magnetic flux density. The pressure sensor 1 is constituted, such that the differential fluid pressure between each of pressure chambers 2 and 3 is calculated on the basis of the detection signal of the hole element 15, while making the signal energized and oscillating at a prescribed frequency and amplitude on the Hall element 15.