Apparatus wherein sheet material is longitudinally step-advanced by alternately being gripped and released in a guide path by a reciprocative gripper, and alternately released and gripped in a gripping station, the sheet material being restrained against buckling from the guide path by guide means adjacent to both of opposite faces of the sheet material, and the guide means enabling the reciprocative gripper gripping the sheet material in the guide path to be operated for effecting a forward feeding stroke having the sheet material released in the gripping station, and subsequently a backward stroke, throughout which latter stroke the reciprocative gripper is in a released condition with reference to the sheet material and the latter is gripped in the gripping station.