PURPOSE: To reduce friction resistance between a rubber mat and a rubbermat placing board and automatically position the rubber mat each time in a defined position by providing a number of air holes on the rubber-mat placing board.

CONSTITUTION: A rubber mat 11 on a rubber-mat placing board 12 is floated up due to the pressure of air which is jetted out of a group ot air holes 12c on the placing board 12 from a lower air jet-out chamber 13, i.e., an air mat. As a result, the friction resistance generated between the rubber mat 11 and the placing board 12 is greatly reduced. By moving pressing boards 17, 18 by means of cylinders 19, 20 in this condition, the rubber mat is pressed from both longitudinal and lateral directions by the pressing boards 17, 18 and brought into contact with the positioning boards 12a, 12b of the placing board 12, thereby, easily and accurately positioning the rubber mat 11 in a defined position.