PURPOSE: To contribute to the high quality of a winding roll by indicating the variation of tension in a roll to be wound by a winder which is the state amount undetectable directly to the operator.

CONSTITUTION: When winding a web to be rewound from a rewind roll over a core 6 journaled by a pair of drum rolls 12, 13 to form a winding roll 7, a reflection tape 10 sticked at the shaft end of a core chuck 9 is detected by a phototube 11 then the output is combined with the output from pulse generators 18, 18a provided on each drum roll 12, 13 and processed to obtain the winding diameter. The winding length is calculated from the output of the pulse generator 18. The winding length corresponding to every predetermined rewind length is compared with predetermined target and to provide the output signal where the difference will be zero to the speed control means for each roll 12, 13 while the winding tension is calculated from said rewind length and winding length then indicated.