To obtain the differential pressure sensor which does not require a power source to detect differential pressure.

The differential pressure sensor is equipped with a pressure sensitive film 7 which has its end part fixed and supported by a fixation part and has a 1st fluid intake space 2a where a 1st fluid 8a flows on the reverse surface side of the pressure sensitive film 7 and a 2nd fluid intake space 2b where a 2nd fluid 8b flows on the top surface side of the pressure sensitive film 7 and detects the differential pressure between the 1st fluid 8a and 2nd fluid 8b from the deformation of the pressure sensitive film 7 while the fluids are put in the fluid intake spaces. The pressure sensitive film 7 is formed of a filmy piezoelectric element 5 which has a reverse-surface side electrode film 4a, a piezoelectric material film 3, and a surface-side electrode film 4b in this order on a thin-film substrate, and the differential pressure between the 1st fluid 8a and 2nd fluid 8b is applied between the top and reverse surfaces of the filmy piezoelectric film 5.