To secure sufficient sensitivity without causing problems of pressure resistance and detection accuracy accompanying this.

This differential pressure sensor comprises a pressure vessel 1 having a first pressure chamber 10A and second pressure chamber 10B, a permanent magnet 52 arranged in the second pressure chamber 10B in a moving manner when pressure difference occurs in the first pressure chamber 10A and second pressure chamber 10B, and a Hall element 60 for detecting the movement of the permanent magnet 52 outside the pressure vessel 1. The Hall element 60 is directly arranged on the outer surface of a wall constituting the second pressure chamber 10B.