PURPOSE: To unnecessitate an oil-pressure cylinder for driving a vacuum pump, by securing either of a cylinder or a piston rod of plunger type vacuum pump composing a vacuum sucking device to the side of bottom force, and the other to the side of top force.

CONSTITUTION: First pipeline 11 and second pipeline 13 are coupled through a change-over valve 12, and fourth pipeline 17 and fifth pipeline 22 are coupled through a change-over valve 16. When, from this state, the piston rod 9 of a mold closing cylinder 5 is extended downwards to execute mold closing operation, a slide bracket 8 falls down and the inside of a vacuum tank 14 is degassed by a vacuum pump 10 driven under interlocking with the mold closing cylinder 5. Then the vacuum tank 14 and a vacuum chamber 20 are coupled, and while the inside of a cavity 3 is degassed, resin material is poured into the cavity 3. The with the flows of air is equallized and the occurrence of air-trap can be prevented.