PURPOSE: To prevent molten resin without fail from being stuck to the whole surface of the exposed side in the radiating plate of a lead frame by setting the surface part of the exposed side to the cavity so that it may be supported under a specific state.

CONSTITUTION: The circumferential edge of the surface part 7a in the radiating plate 7 of a lead frame 6 and the circumferential edge 9a of a cavity part 9 are welded under pressure when the dies are closed and the surface part 7a is held by the upper side of the holding body 8 to be held on the same level as the cavity bottom. The molten resin A can be prevented from entering the cavity part 9, the lead frame side does not bend or deform to the side of the cavity part 9 and the permeated molten resin A can be prevented from being stuck all over the side of the surface part 7a.