PURPOSE: To obtain a fluid oscillation detector for preventing looseness of piezoelectric film support and crushing and the other looseness of a piezoelectric film and capable of equipping a differential primary element superior in temperature characteristics.

CONSTITUTION: A fluid oscillation detector 10 consists of a first housing 1, a second housing 2, a joint part 4, a piezoelectric film 3, a first pressure chamber and a second pressure chamber 8, the first housing 1 has a recess part for forming the first pressure chamber 7 and a communicating hole 5 communicating with the outside in the recess part and the second housing 2 possesses another recess part for forming the second pressure chamber 8 and another communicating hole 6 communicating with the outside in the recess part. The joint part 4 supports the piezoelectric film 3 in a space part, in which the first and second housings 1, 2 are mutually bonded, exclusive of both the recess parts so that the first and second recess parts may be opposed to each other and which is formed with the opposed recess parts, and the piezoelectric film 3 matches the first and second housings with their coefficients of thermal expansion and the circumferential edge parts thereof are supported and fixed on the joint part 4.