To continuously execute heat-treatment of a steel wire by overlapping loops of a steel wire to form a wire coil, covering the coil with a thermally insulating hood, transferring the coil to a heating unit or a cooling unit by a horizontal conveyor and an intermediate conveyor and then delivering the same to a wire coil delivering unit.

The steel wire D which is drawing-processed by a hot rolling unit is cooled by a cooling unit V and then is formed in a loop-shape by a winding laying unit WL and is overlapped by a coil collecting unit WS2 to form a wire coil DB. The wire coil DB is placed on a pallet 2 on a transverse conveyor QF1 and is covered with the thermally insulating hood 1 by a laying unit 3. The hood 1 is subjected to the heat-treatment by hot air from a blower 12 while transportation by a horizontal conveyor HF and then is delivered to other transportation unit 10. Otherwise, the wire coil DB covered with the hood 1 is carried into an immersing bath 5 via an intermediate conveyor 4 to be cooled and then is delivered to the other transportation unit 10 by the delivering unit 9 or is positioned in front of a collecting pool 6 by the transverse conveyor QF1, is heat-treated in a heating unit and then is delivered to the other transportation unit 10 by placing the wire coil on the wire coil delivering unit 9 via the intermediate conveyor 8.