PURPOSE: To prevent resin from sticking to the internal surface of a pot by providing a plunger, through a circumferential ring made of elastic material, in the pot which is interconnected, through a resin supply passage, to a cavity for accommodating an object to be sealed.

CONSTITUTION: A resin tablet is thrown in the pot 5 of a metal mold for sealing resin 10 and it is smashed by causing a plunger 6 to descend, and by this, it is possible to push the resin into a cavity wherein an object to be sealed is accommodated quckly by preveting resin from sticking to the internal surface of the pot 5. As a circumferential ring 7 is caused to closely contact with the internal surface of the pot 5, the resin is substantially prevented from sticking to the internal surface, and even if resin is caused to stick to the internal surface of the pot 5 by the plunger 6 as it is pulled up, the amount of resin is very small and it can be easily removed by the scraping action of the circumferential ring 7 when the plunger 6 is made to descend next time.