A method for printing an image onto both sides of a sheet, comprising: using a sheet having perforations formed at both ends of the sheet for sheet feed; using a feeder including a drive roller and two pin tractors, the drive roller rotating to drive the sheet in contact with the sheet, and the pin tractors including a plurality of pins to engage the perforations and being disposed in both ends of the drive roller to rotate to drive the sheet with a coaxial rotational driving force with the drive roller; disposing the sheet in the feeder, and, in this state conveying the sheet synchronously with movement of the pins to print an image onto one side of the sheet; and turning the sheet, onto one side of which printing has been performed, inside out and is disposed in the feeder, and, in this state, convening the sheet synchronously with the movement of the pins to print an image onto another side of the characterized by the fact that the pin is formed to have a shape which makes a movement distance of a front of the pin on a line along a conveyance direction of the sheet equal to a movement distance of a front base position of the pin, and an inner diameter of the perforation and an outer diameter of the pin at a bottom position establish a relationship of DA > DN, a gap is provided between a rear of the pin and a rear rim of the perforation, and the pin is so formed as to move, during a period from when the pin engages the perforation to when the pin is disengaged from the perforation, in a direction which allows the front of the pin to be disengaged from the perforation in contact with a front rim of the perforation. using a sheet having perforations formed at both ends of the sheet for sheet feed; using a feeder including a drive roller and two pin tractors, the drive roller rotating to drive the sheet in contact with the sheet, and the pin tractors including a plurality of pins to engage the perforations and being disposed in both ends of the drive roller to rotate to drive the sheet with a coaxial rotational driving force with the drive roller; disposing the sheet in the feeder, and, in this state conveying the sheet synchronously with movement of the pins to print an image onto one side of the sheet; and turning the sheet, onto one side of which printing has been performed, inside out and is disposed in the feeder, and, in this state, convening the sheet synchronously with the movement of the pins to print an image onto another side of the characterized by the fact that the pin is formed to have a shape which makes a movement distance of a front of the pin on a line along a conveyance direction of the sheet equal to a movement distance of a front base position of the pin, and an inner diameter of the perforation and an outer diameter of the pin at a bottom position establish a relationship of DA > DN, a gap is provided between a rear of the pin and a rear rim of the perforation, and the pin is so formed as to move, during a period from when the pin engages the perforation to when the pin is disengaged from the perforation, in a direction which allows the front of the pin to be disengaged from the perforation in contact with a front rim of the perforation.