PURPOSE: To detect wrinkle occurrence limit of a film bridged between roles in a film feeding line.

CONSTITUTION: In a detecting method for wrinkle occurrence limit of a film 1, two roles 12 and 13 are horizontally supported, parallel to each other and with a specified space between roles while permitted free rotation, and the film 1 is bridged between the roles 12 and 13, and further, one end of the film 1 is fixed with the other end applied with a load, so that a wrinkle occurrence limit value is detected based upon the load when longitudinal wrinkle occurs on the film 1.