PURPOSE: To sense a force woring on a roll even when a rotary cylindrical member wherein a tensional web passes through is a driving or play roll by fitting the front end of a beam member in an automatic aligning type ball bearing inside a cylindrical housing.

CONSTITUTION: A cylindrical projection 16 of a beam member 11 is surrounded by automatic aligning type ball bearings 35. An outer race 37 has a circular tray type bearing surface, thereby permitting entire adjustment of relative movement so as to allow mismatch of frame member and alight bending of the member 11. A space type waveform spring 42 allows a bearing 35 to move slightly in an axial direction against a cylindrical housing 40 surrounding the bearing 35. Thus, the movement can correspond to the expansion of roller during preheating. The housing 40 is received within the end part of a roll, to which a force generated by a tensional web moving on the outer surface of the roll is applied. This force is transmitted to the beam member 11, and a strain on a beam 14 of the beam member 11 is sensed by a strain gauge 17, then its electric signal is sent to a controller.