Projecting ends of terminal conductors projecting out of a thick portion of a holder and electrode terminals of a flow rate detecting element are electrically connected by bonding wires. A peripheral wall member is secured by an adhesive to a thin portion of the holder and the flow rate detecting element so as to surround the electrical connection portions between the projecting ends and the bonding wires and between the electrode terminals and the bonding wires. A gel is formed so as to seal the electrical connection portions, and a rubber is injected into and cured inside the peripheral wall member so as to seal the gel.