Seal surfaces in three directions of a base and a cover are mutually fitted as a first seal part in combination of concave threads and convex threads, and sandwich three sides of a circuit board between an innermost peripheral part convex thread at the base side and an innermost peripheral part concave thread at the cover side. A connector member having a second seal part is fixed to one side of the circuit board, a concavo-convex seal surface between the base and the connector member is located on a low step surface, and the concave and convex threads on the seal surface of the connector member provided on the base pass the concave and convex threads of the seal surface in the three directions each other to be continuous.