A sensor assembly includes a sensor chip, a circuit board, and a wire holding case. The wire holding case holds a bonding wire, which connects the sensor chip with the circuit board. The wire holding case is inserted in an insertion hole of a case. The wire holding case has a low rigidity portion and a high rigidity portion in an X direction. The low rigidity portion has a space accommodating the bonding wire. The high rigidity portion has a reference surface in contact with an inner periphery of the insertion hole to position the wire holding case in a Y direction. The high rigidity portion has a surface on the opposite side of the reference surface in the Y direction. The surface is biased from a projection, which is formed on the inner periphery of the insertion hole, in the Y direction.