PURPOSE: To prevent air-bubbles from being caused between a steel sheet pile and a plastic sheet, and to enhance the yield of final products by preforming the plastic sheet into a steel sheet pile shape, and by carrying out the process of sticking the plastic sheet on the steel sheet pile in a vacuum atmosphere.

CONSTITUTION: The operation of a vacuum pump 23 is started in a state that sealing devices 21, 22 are closed prior to the admission of a steel sheet pile 9, and air in a vacuum chamber 20 is discharged until the steel sheet pile 9 enters. When the steel sheet pile 9 enters, the sealing device 21 on the front surface of the vacuum chamber 20 is opened to such an extent that corresponds to a gap through which the steel sheet pile 9 can be entered, and the sealing device 21 is put into a closed state simultaneously with the admission of the steel sheet pile 9. On the other hand, a plastic sheet 1 is fed by a feeder roll 5 while being restricted by a sheet side guide 14, and the feed of the plastic sheet 1 is once stopped at a point of time when the leading end thereof comes beneath a first sheet-sticking roll 11. Then, in a state that the top end of the steel sheet pile 9 has been moved to a position beneath the first sheet- sticking roll 11, said roll 11 is lowered and starts to stick the plastic sheet on the steel sheet pile. Thereafter, the plastic sheet is stuck on the steel sheet pile by second and third sheet-sticking rolls 12, 13 in sequence..