To provide a converter which restrains the development of sloshing on molten metal bath surface in a lowing operation of a bottom-blown converter or a combination-blown converter, particularly even under high speed blowing condition, and reduces metal sticking quantity on the furnace opening part caused by the development of spitting and can give uniform mixing stir more intense than action with top-blown jet and bottom-blown bubble spout to the bath, and a to provide a blowing operational method.

The bottom-blown converter or the combination-blown converter is constituted of plural side-blow tuyeres 7 having an angle θ formed between gas blowing direction and the tangential direction of the inner peripheral circle of a side wall of 0°<θ<θ90°, strain gages 14 for detecting the strain of the furnace shell near the side-blown tuyeres, an instrument 15 for detecting a dynamic strain (acceleration) of the furnace shell in the radial direction of the furnace obtd. from the strain gage and a device 16 for analyzing natural frequency of the molten metal bath from the frequency of the furnace shell having the above acceleration. Then, in the blowing operational method of restraining the sloshing on the molten metal bath surface by using this converter, the natural frequency of the molten metal bath obtd with the frequency analyzing device 16 and successively, the blowing gas rate for each side blow tuyere obtd. in the specific formula is periodically controlled.