PURPOSE: To lessen the force required for caulking by dividing plural bending rollers to plural groups each consisting of one or plural pieces thereof, and bending and caulking successively tongue parts by each group according to the sliding of sliding bars.

CONSTITUTION: Tongue parts 2 provided to both ends of baffles 1 are passed through paired side plates 3 and the projecting parts 2 are bent and caulked by bending rollers 9, 10. Plural bending rollers 9, 10 are provided to the respective paired sliding bars 5, 6 which are driven to slide in the directions opposite from each other in the stage of caulking. The plural rolls 9, 10 are divided to plural groups each consisting of one or plural pieces thereof. The parts 2 are bent and caulked successively by each group by the rollers 9, 10 belonging to said group according to the sliding of the bars 5, 6.