To release a float from a mooring arrangement only by giving a series of different frequency signals thereto in predetermined order.

This device includes circuits 110, 120, 130, 140 for selecting frequency components contained in low frequency signals from a receiving circuit RCV to feed output signals, first detecting circuits 111, 121, 131, 141 of which plural pairs output operation command signals after output signals are given thereto and second detecting circuits 112, 122, 132, 142 for outputting non-operation command signals. A detecting circuit train to which the first detecting circuits are connected so as to give operation command signals to the first detecting circuits in next order in accordance with predetermined order and to which the respective second detecting circuits are connected so as to give non-operation command signals to the first detecting circuits out of operation order in accordance with predetermined order for forming output signals during operation in accordance with predetermined order, and a releasing means for driving a motor M, when the output signals are given by the detecting circuit train, to release a mooring arrangement.