A hot dip coating apparatus and method, enables stable and continuous production of a coated steel strip having a high degree of uniformity of the coating quality over the breadth of the steel strip and clean coated surfaces free of deposition of dross. The hot dip coating apparatus has a bottom slit through which a steel strip to be coated is introduced and pulled upward through the coating tank, and an electromagnetic sealing device which applies a magnetic field to the molten metal in the coating tank so as to hold the molten metal inside the tank. The coating tank is provided at its top with an overflow dam for allowing the molten metal to overflow out of the coating tank. The apparatus also has a molten metal supply system which produces a circulating flow of the molten metal through the coating tank. The molten metal supply system has molten metal buffers which communicate with a molten metal supply passage and from which the molten metal is discharged towards the steel strip.