Technologies to convert biomass to liquid hydrocarbon fuels are currently being developed to decrease our carbon footprint and increase use of renewable fuels. The printed products are introduced into the grippers in groups without any change in the spacing between successive printed products, and the conveying speeds of the feed conveyor and the removal conveyor are coordinated such that the portion of each group of products which projects into a gripper is less than the depth of the mouth of the gripper. The recess part has an outermost bottom surface and an inner side surface formed continuously between the bottom surface and the inner surface of the wall of the container. The free magnetic layer is located close to the top face of the magneto-resistance element. The current control circuit controls the value so that a voltage difference between both ends of the first resistor becomes equal to a predetermined value.