PURPOSE: To enable the correction of register or the adjustment of a tensioned sheet by curving a support for parallelly provided sheet grippers extending at a right angle to the advance direction of a sheet on the basis of the operation cycle of a machine.

CONSTITUTION: The end part of a gripper bridge having a U-shaped cross section extending laterally over machine width is fixed to a rigid lever 9 and this lever is fixed to the revolving shaft 10 of a front gripper device on the other side thereof. The curving device for the gripper bridge 8 is provided to the lateral support 11 of a machine frame and composed of the stopper 12 cooperating with the opposed stopper 13 of the gripper bridge 8. In order to correct register, the stopper 12 can move on a connection line straightly by the operation of an adjusting screw 14 and the bending of the gripper bridge 8 is made large or small. The grippers 30 movable around the revolving shaft 19 surround widely at an edge part corresponding to the bending degree and the still more large acceleration of a sheet is performed at the edge part to tension the sheet.