PURPOSE: To prevent occurrence of dent and ruggedness transfer flaws on the surface of the metallic strip caused by the oxidized scales which arc produced on the surface of the metallic strip, dropped and are adhered on the surface of the supporting roll as the adhesion or make the rugged surface of the supporting roll in annealing the metallic strip which is continuously passed in a catenary type annealing furnace of open-air and direct fire system.

CONSTITUTION: A metallic strip S which is continuously passed while being supported by each supporting roll 2 to be protected from the high atmospheric temperature in the furnace by a water-cooled lintel 3 is annealed in a catenary type annealing furnace 1 of open-air direct fire system. The high atmospheric temperature gas extracted from the outlet side zone of the furnace 1 is blown against the lower surface of the metallic strip S immediately before being abutted on the supporting roll 2 from the injection nozzle 4 arranged at the upper end part on the furnace inlet side of the water-cooled lintel 3 at the pressure of 500-700mm water head with the flow speed of 3-5m/sec to drop the oxidized scale produced on the lower surface of the metallic strip S before being abutted on the supporting roll 2.