PURPOSE:To easily and surely give a constant tension to a plate by giving a tension to a plate by pinching it between a pressing roller and braking roller and controlling the solenoid brake controlling a braking roller by measuring this tension. CONSTITUTION:A plate 35 is fed continuously between a pair of forming rolls 37, 39 after a constant tension being given by pinching it between a pressing roller 49 and braking roller 51, and the corrugated fine 41 formed in a wavy shape is obtd. The tension given on the plate 35 is measured by detecting the load in the upper direction acting on the probe 71 of a tension measuring instrument 45 and the value of this tension is inputted to a controller 47. The value of the tension measured by the tension measuring instrument 45 and preset value are compared in the controller 47, the voltage of the solenoid brake 69 controlling the braking roller 51 is fluctuated by the value equivalent to the difference in these tension values and a constant tension is given to the plate 35.
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