PURPOSE: To prevent surely a pinhole defect by adding directly a dehydrogenation accelerator consisting essentially of an iron oxide or aluminum oxide into the steel near the immersion nozzle in a mold under casting.

CONSTITUTION: A molten steel 3 is supplied from the immersion nozzle 1 to a mold 2 to cast continuously a steel for enamel. A hooped conduit pipe 4 is immersed into the steel near the nozzle 1 and the dehydrogenation accelerator 5 consisting essentially of the iron oxide or aluminum oxide which evaporates the hydrogen dissolved in the steel 3 is supplied by a supply device 6 to the pipe 4 from which the accelerator is added to the steel 3.