A portable equipment detecting system includes an antenna having a first element of which a longitudinal direction is defined as a running direction of the vehicle, a second element of which longitudinal direction is defined as a direction perpendicular to the running direction of the vehicle and the vertical direction of the vehicle, and a bypass wiring of which one end is connected to a connection point between the first and second elements; and detecting circuit adapted to switch between three power-supplied states of the antenna including a first supplied state, a second supplied state and a third supplied state, and to detect a location of the portable equipment based on an acknowledge signal from the portable equipment when the power-supplied state is switched.