PURPOSE: To confirm the running state of gas and obtain safety by rotating blades with running gas and providing a fluid sensor which generates a sound at a proper position in piping.

CONSTITUTION: The sensor 6 is provided with a partition wall 3 to form a gas running chamber 4 and a sound generation chamber 5. A transparent upper lid 1 is fitted to this sensor 6 and blades 10 are provided. When the gas glows in the gas running chamber 4 through an intake 7, the blades 10 rotate, which is seen through the upper lid 1. The rotation of the blades 10 turn the windmill 18 in the sound generation chamber 5 through the engagement among plural gears. Thus, the windmill 18 rotates to generate a sound. This fluid sensor 6 is provided at a proper position in a gas piping circuit. Consequently, the running of the gas is confirmed through the sensor visually and audibly, namely, by the rotation of the blades and the sound of the windmill, so a leak in the gas piping is detected immediately.