PURPOSE: To control plate thickness without making control between stands and draft setting intricate by setting roll gaps and making the rolling reduction of the lowermost stand zero so that the plate thickness on the outlet side of the (n-1)th stand attains target plate thickness.

CONSTITUTION: Screw down devices 3eW3a are so set by a roll gap control device 1 that the plate thickness on the outlet side of a rolling mill 4b attains the target plate thickness after a change in the stage of tandem rolling by rolling mills 4aW4e. The length of a rolling material is measured by an arithmetic unit 6a for the length of the rolling material and the device 3a is moved to make the rolling reduction of the stand 4a zero so that the rolling load on the operating side of the stand 4a and the rolling load on the counter operating side, measured by a rolling load detector 2a, are made equal when the desired change point of the plate thickness arrives at the mill 4a. The speed reference taking into the forward slip of the mill 4b into consideration is calculated by an arithmetic unit 9 for speed and is outputted to a speed control device 7. The load is dispersed to the mills 4bW4c by draft control.