To accurately measure the flow rate of a fluid number test, even using a flow sensor the output characteristic of which may vary, depending on the kind or composition of the fluid.

When a microheater 4 heats a drive current from outside, an upstream thermopile 8 detects the temperature of a fluid before being heated by the microheater 4 in parallel to the microheater 4 heating and outputs a first temperature detect signal, a downstream thermopile 5 detects the temperature of the fluid before being heated by the microheater 4 and outputs a second temperature detect signal, and the flow rate is calculated, based on the difference signal between both detect signals. A right and left thermopiles 11, 13 disposed in a direction approximately perpendicular to the flowing direction of the fluid to the microheater 4 detect the temperature of the fluid flow to output a right and left temperature detect signals and the calculated flow rate can be corrected, based on physical property values calculated, based thereon.