To accurately control a molten metal level in the mold of continuous molding facilities in a preset position by improving the responsiveness and follow-up ability of a hydraulic cylinder.

A hydraulic cylinder 3 adjusts the flow rate of molten metal by driving a stopper 16 as a tandish opening/closing means. A vibrator 4 reduces sliding resistance at the time of starting the hydraulic cylinder 3 by providing vibration to the same. A molten metal level detector 9 detects the molten metal level in a mold and a computing unit 10 calculates, based on the detected molten metal level, the objective position of the stopper 16. A position detecting means 5 detects the position of the stopper 16 and a servo valve controller 7 sends a driving command to a servo valve 6 so as to place the stopper 16 in the objective position. The servo valve 6 sends hydraulic oil to the hydraulic cylinder 3 and thus the molten metal level in the mold is controlled in a preset position.