PURPOSE: To allow diameter- and full-close controlling to be performed according to the levels of the tundish without nozzle clogging and erosion, etc. of cross gate hole by making the number of revolutions in the forward and backward revolving directions the same in selecting the large diameter and small diameter of each cross gate hole of a rotary type slide plate.

CONSTITUTION: When the tundish level exceeds the upper limit in the rotary type slide plate opening-closing device provided to continuous casting equipment, the rotary plate is rotated so as to select a small diameter if the current bore is of a large diameter and so as to select close if the current level is of a small diameter, whereby the level is controlled. When the level exceeds the lower limit, a small diameter is selected if the current is fully closed and a large diameter is selected if the current is of a small diameter. When the close state is continued over a long time, it is shifted to a small diameter by setting of the full-close time. In the case of shifting from the full-close state I to the small-diameter state II, the rotating direction is reversed and shifting is done without going through the large diameter. With respec to to the bore, the numbers of forward and backward revolutions are made the same to prevent the uneven wear of the cross gate port of the sliding plate.