PURPOSE : To prevent the discoloration of sheet steel surfaces by pickling the sheet steel coil taken out from an annealing furnace been neutralizing the same with an alkaline soln. thereby passivating the sheet steel surfaces. CONSTITUTION : When the coil 2 under cooling in the inner cover 1 of an annealing furnace cools down to below 400 deg.C, the inner cover 1 is removed and the coil is allowed to cool in the atmosphere down to temp. above 100 deg.C. Thence, it is placed on a conveyor 4 by a down ender 3, and is sent to uncoiling machines 5, 6, whereby it is uncoiled. The leading end of the uncoiled sheet steel 2 is connected to the trailing end of the preceding coil by a connector 7 and is sent continuously to a pickling device 8. Here, it is removed of oxide films by spray pickling and is rinsed in a rinsing tank 9, thence it is sent into an alkali neutralizing tank 10, where it is subjected to passivation treatment. Further, it is washed in a rinsing tank 10, is skin- pass-rolled by a skin-pass rolling mill 12, passes through a parting shear 13 and an oiler 14 and is coiled by coilers 15, 16.