PURPOSE: To automatically control the sucking force of a suction fan so that a work sheet can securely move along the surface of a platen.

CONSTITUTION: In the part adjacent to a line drawing position on a work sheet F on a platen 2 small suction-holes 3 for sucking the sheet are provided, and the work sheet F is sandwiched between the grid roll 4A exposed from the platen 2 and the pinch rollers 4a and 4b arranged thereon. The work sheet F is moved by means of the grid roll 4A and the pinch rollers as the work sheet F is sucked on the surface of the platen 2 by means of a suction fan 10. The width of the work sheet F is detected by a sensor 18, and the suction fan 10 is controlled so that the number of its rotations increases almost in inverse proportion to the width.