PURPOSE: To easily provide sealing agent to a joint between a case main body and a lid in a short time.

CONSTITUTION: A lid 4 is so curved as to slope smoothly downward from its center to circumferential edge 10, the lid 4 is internally inserted to the opening edge 6 of a case main body 2, sealing agent 11 is made to drop on the center of the lid 4 to flow down over its outer surface, and the agent 11 is made to spread over the joint between the opening edge 6 of the case main body 2 and the circumferential edge 10 of the lid 4. Furthermore, a sealing agent guiding groove which slopes smoothly downward from the center to the circumferential edge of the lid 4 is provided to the lid 4, the lid 4 is internally inserted to the opening edge 6 of a case main body 2, then sealing agent 11 is made to drop on the center of the lid 4 and spread over the joint between the opening edge 6 of the case main body 2 and the circumferential edge 10 of the lid 4 through the sealing agent guiding groove.