PURPOSE: To prevent sagging of resin to a contact part with an electrode plate when protective resin is cast by airtightly holding an outer periphery of a semiconductor base via a cavity by upper and lower cases.

CONSTITUTION: An upper cast mold 2 made of heat resistant resin and a lower cast mold 3 made of heat resistant resin are respectively assembled with upper and lower cases 4, 5. In this case, the molds 2, 3 form an airtight cavity 6 together with semiconductor base 1 when the base 1 is held. Two through holes 7, 8 are respectively provided at the case 4 and the mold 2 assembled with the case 4 to communicate with the cavity 6. Thus, the resin is not sagged out of the cavity at the time of casting the resin, and the resin can be formed on an outer periphery 21 of the base.