PURPOSE: To enable control to make uniform a tapping temp. of each strand of a tundish having three strands furnished with a plasma heating device.

CONSTITUTION: In the tundish 4 having three strands 1, 2, 3 furnished with a plasma heating device 6, a opening area A of a gate 7 arranged in a molten metal flow passage and an installation position of the plasma heating device 6 are controlled to make uniform a tapping temp. of each strand. Accordingly, by making uniform the tapping temp. of each strand, the quality of ingots among three strands is made uniform, also making low temp. casting possible.