PURPOSE: To surely defoam a high-viscosity resin by placing a vessel contg. a resin to be defoamed in a hermetically sealable defoaming vessel main body, depressurizing the main body by an evacuating means, and providing a foam breaking means to be brought into contact with the film surface of the bubbles generated in the resin.

CONSTITUTION: The foam breaking device 11 is fixed to the vessel 9 contg. a resin 8, the vessel 9 is set in the defoaming vessel main body 1, a lid 3 for the main body 1 is closed, and the main body 1 is hermetically sealed. A vacuum pump 7 is then operated to evacuate the main body 1, and air bubbles are generated in the resin 8. The tip 12 of the foam breaking device 11 is brought into contact with the film surface of the bubbles, hence the film surface is broken, and the air in the bubble is discharged.