PURPOSE: To calculate a tension additional amount owing to inertia of a plate and a carrier rule itself based on a plate conveyance speed, the rotation speed of a carrier roll, a plate weight, and an inertia moment and to suppress production of a tension fluctuation through correction of a torque reference based on a calculating result.

CONSTITUTION: When no tension fluctuation of a plate is produced, control of torque is made on a plate conveyance mechanism 11 so that the conveyance speed Vd on the output side of a plate is adjusted to a value approximately equal to a conveyance speed reference VREFd. When a tension is fluctuated, the tension of a plate on the output side of loop car equipment is detected by a tension detector 5 and based on a deviation between the detecting tension value of a plate l and a tension reference set by a tension setter 6, the conveyance speed reference VREFd is correct%Based on the corrected value, a torque reference is determined by a speed control circuit 9. The torque reference is corrected by an addition part 23 by using an adjustable speed compensating amount calculated by an adjusted speed compensating circuit 22. Based on the corrected torque reference, torque control is applied on the plate conveying mechanism 11 by a torque control circuit 10.