PURPOSE: To control the amount of metal stuck to a steel strip by hot dipping to a predetermined value in all points by performing feedback control whenever the strip moves by a length equal to the distance from the position of a nozzle for spraying a hot dipping amount controlling gas to the position of a hot dipping amount detector when the strip is hot dipped continuously.

CONSTITUTION: When steel strip 2 is galvanized continuously by passing through molten Zn bath 1, feedforward control for setting the pressure of nozzle 3 for spraying a galvanizing amount controlling gas in accordance with a set galvanizing amount and the speed of strip 2 passing through bath 1 is combined with feedback control for controlling the gas pressure of nozzle 3 in accordance with the difference between the set and measured values of galvanizing amount, controlling the amount of molten Zn stuck to strip 2. Whenever strip 2 moves by a length equal to the distance from the position of nozzle 3 to the position of galvanizing amount detector 5, the actual galvanizing amount is obtd. by scanning in the lateral direction with detector 5 and in accordance with the difference between the measured valves at central and edge portions the spraying pressure of nozzle 3 is regulated to stick the desired amount of Zn to the whole surface of the strip.