A detector for a proximity sensor, includes: a sensing portion including a pair of sensing coils which has central axes along a direction intersecting with a moving direction of a sensed object moving in a predetermined moving path and is provided so as to interpose the moving path; a circuit block including a capacitor composing an LC resonant circuit with the sensing coils of the sensing portion and provided with an oscillator which oscillates the LC resonant circuit; and an electric connector composed of first connection terminals and a first conductor pattern that connect the sensing coils of the sensing portion in series, and second connection terminals and a second conductor pattern that connect the sensing coils to the oscillator.