PURPOSE: To control plate thickness through a value given by a thickness indicator when there is no disturbance such as a partial deformation of a roll and to provide a automatic plate thickness controller which can recognize the disturbance when it is found.

CONSTITUTION: This device is provided with an inlet side profile meter 21 which is equipped on the inlet side of a mill 1 and detects a plate profile in the plate width direction, an outlet side profile meter 31 which is equipped on the outlet side of the mill and detects the plate profile in the plate width direction and a plate thickness controlling means 7 which compares the inlet side plate profile with the outlet side plate profile detected by the inlet side and outlet side profile meters with a moving quantity of plate as a parameter at the same measuring position, calculates a quantity of deviation from the set value and outputs the rolling-down control signal through the quantity of deviation to a rolling-down controller 6.