A battery-operated object detecting device (D) includes a detecting unit (U) adapted to be driven by an electric cell (12) mounted thereon, and a transmitting device (20) driven by the electric cell (12) in the detecting unit (U) for wireless transmitting at least a low battery signal being indicative of a reduction in voltage of the electric cell (12). An electric power sharing unit (30) for outputting a supply voltage to the transmitting device (20) includes a voltage changing circuit (32) for changing, based on a low battery detection result from a low battery detecting circuit (13), to a voltage necessary for causing a low battery determining circuit (21) of the transmitting device (20) to change the supply voltage from the electric cell (12) to a voltage for determining a low battery state.