PURPOSE: To replace defective parts of a hybrid integrated circuit before a metallic case is bonded, by performing the burn-in operation of the hybrid integrated circuit in protective box wherein inert gas is sealed, and extracting defection in an early stage.

CONSTITUTION: On the center projecting part 10' of a protective box body 10, the metallic stem 1 of a hybrid integrated circuit is held. This body 10 is provided with a suction pipe 15 and a suction pipe 16 and in the protective box wherein inert gas is sealed, the hybrid integrated circuit is burned in through an airtight terminal 14, a connector 13, etc. to test its characteristics, thus extracting defective in an early stage. Therefore, before a metallic case 4 is bonded, parts such as defective active element 3 are replaced, generating the hybrid integrated circuit efficiently.