To demonstrate a stable function without being affected by a conductor by providing the conductor for reacting to output signals near a resonance circuit equipped inside a housing and setting the resonance circuit constant of the resonance circuit in the state of considering the effect of the conductor.

Inside the housing 1, conducting members 7 and 9 are respectively installed on the bottom surface side of an upper case 3 and the bottom surface side of a lower case 5. Also, inside the housing 1, a circuit board 11 is installed between the conducting members 7 and 9. Then, the conducting members 7 and 9 are equipped inside the housing 1 beforehand and the resonance circuit constant of a reception circuit pattern (LC resonance circuit) 13 is decided in the state. That is, by deciding the resonance circuit constant of the reception circuit pattern (LC resonance circuit) 13 in the state of considering the effect of the conducting members 7 and 9 beforehand, the characteristics are prevented from changing even when an external conductor is present near the outside at the time of use.