To accelerate time until resin in a cull-remaining part is cured by a method wherein a shape of the cull-remaining part is made non-cylindrical to increase a value of a ratio of surface area to volume, ad heat from a mold is made further easy to received.

A cull-remaining part 14 formed above a pot 3 housing a tablet 2 consisting of thermosetting resin in a mold 10 has a non-cylindrical shape, for example, a regular square pole shape, and a value of a ratio of surface area to volume is increased. A tablet 2 in the pot 3 is pushed up with a plunager 8, made to flow by melting by heat from the mold 10, sent by pressure into each cavity 5 through the cull-remaining part 14, a runner 6, and a gate 7, and the molten resin is cured to seal a semiconductor element being an object to be sealed. Since a value of the ratio of the surface area to the volume of the cull-remaining part 14 is large, the tablet 2 becomes further easy to receive heat from the mold 10, time until the resin in the cull-remaining part 14 is cured is accelerated, and productivity of the semiconductor element is improved.