PURPOSE: To provide a fluid sensor which has a simple structure without forming a fluid retention part and can detect pressure, flow rate, temperature, etc.

CONSTITUTION: An annular partition wall 18 raised at a center of a chamber 12 is provided while forming a channel 19 continued to a first fluid exit/entrance 15 in a body 10 formed with the chamber 12 between the exit/entrance 15 and a second fluid exit/entrance 16. Thus, an inner inlet 20 opened on the way in the chamber 12 and an annular channel 21 communicating with the second exit/entrance 16 are formed concentrically in a circular state, and a sensitivity detector 23 is provided thereon.