Abstract: A marking device is described which includes a guide post having a guide surface and inclined to the vertical plane, a horizontal arm carried by the guide post and movable up and down along said guide surface, a detector for detecting the material on which the marking is to be effected and carried by the horizontal arm, movable back and forth in the direction perpendicular to the material, a crosshead movable along the length of the horizontal arm, a marking head carried by the crosshead movable in the direction perpendicular to the direction in which the crosshead, is moved and a marking member carried by the marking head, movable in the direction perpendicular to the directions in which the crosshead and the marking head are moved, respectively.