Abstract: When a micro-heater heats fluid using an external driving current, an upstream thermopile 8 detects the temperature of the fluid before it is heated to produce a first temperature detected signal and a downstream thermopile 9 detects the temperature of the fluid before it is heated to produce a second temperature detected signal. The flow rate is computed based on the difference signal between both detected signals. A right thermopile 11 and a left thermopile 13, which are arranged in a direction orthogonal to the flow direction of the fluid, detect the temperature of the fluid to produce a right temperature detected signal and a left temperature detected signal. The property of the fluid is computed on these right and left temperature detected signals. The flow rate is corrected on the basis of the property thus computed. The flow rate of an object fluid for measurement can be accurately measured by a flow sensor whose output characteristic varies when the kind or composition of the fluid changes.