A board mounting thereon a measuring chip is fixed to a body in close contact relation to form a main passage and a sensor passage inside of the body, while a hot wire for a temp. sensor and a hot wire for a flow velocity sensor, both being provided on the measuring chip, are bridged across the sensor passage, to measure the flow rate of a gas flowing in the inside of the body by means of an electric circuit on the back side of the board. In a state where an electrode for a hot wire on the measuring chip is joined to an electrode for the electric circuit on the board, the temp. sensor hot wire and the flow velocity sensor hot wire both provided on the measuring chip are connected to the electric circuit on the back side of the board.