FLOW RATE DETECTOR

A flow rate detector includes: a housing; and a substrate assembly disposed in the housing. The substrate assembly has a flow rate detection element, a temperature detection element, and a circuit board on which the flow rate detection element and the temperature detection element are mounted. The circuit board includes a body portion fixed to the housing, and a protrusion extended to protrude from the body portion. The protrusion has an element fix portion to which the temperature detection element is fixed. The protrusion has a supported portion within a supported range including a position of the element fix portion. The supported range is defined from the element fix portion to a tip end of the protrusion along an extension direction of the protrusion. The supported portion is supported by the housing to suppress a displacement of the element fix portion in a thickness direction of the circuit board.