PURPOSE: To position a horizontal scale at a position separated from a drawing board by single operation.

CONSTITUTION: A slider 20 is attached freely movably to a guide rail 11, a scale arm 40 is mounted rotatably on a rotary shaft fixed to the slider 20, and a horizontal rail 18 to which a horizontal scale 19 is fixed is fixed to the scale arm 40. In a state in which the horizontal scale 19 is brought into contact with a drawing board 10, when an operation member 71 is pushed, the scale arm 40 is rotated to position the horizontal scale 19 at a position separated from the drawing board 10.