PROBLEM TO BE SOLVED: To provide a plate thickness controller for a tandem rolling mill whose plate speed accuracy in a whole speed area including that at the time of low speed rolling is improved. SOLUTION: By using the integrated value of rolling distance actual results detected by range finders 50 to 54 installed on the outlet side and the inlet side of each stand of a tandem rolling mill and on the outlet side of bridle rolls and plate thickness actual result values detected by plate thickness meters 60 to 64, a mass flow operation is performed. A plate thickness actual result value just under the roll of a stand, which has been found by the operation, and the deviation in a target plate thickness, are set as the speed correction quantities of each stand. And, they are added to the speed command values of each stand, which are the outputs of speed command devices 30 to 34, are sent to motor controllers 20 to 24, and make motors 10 to 14 revolve.
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