PURPOSE: To maintain always optimum short side tapers of a mold automatically in accordance with detection values by providing a controller for short sides of molds having distance sensors for detecting the change in the shape of an ingot.

CONSTITUTION: The molten metal 4 cast in a mold 2 consisting of long sides 2A and movable short sides 2B forms a solidified shell 6 to an ingot which is drawn downward. Plural pieces of distance sensors 8 disposed right under the short sides 2B detect the fluctuations in the distances from the surface of the ingot, and in accordance with the signals thereof, a distance meter controller 10 feeds the profile information on the shape of the short sides to the next short side taper controller 12. The controller 12 instructs an oil hydraulic unit 14 in accordance with the input to engage or disengage a clutch 20 via an oil hydraulic cylinder 18. Further it instructs a driving controller 16 to run an electric motor 2 forward or backward and to advance or retreat the bottom ends of the short sides 2B with a speed reducer 24, thereby changing and correcting the short side tapers.