PURPOSE: To make the number of component parts small, and improve the safety and impact resistance.

CONSTITUTION: Plural edge bearing springs 2 are provided at a terminal plate 1 for forming a ground side pole edge bearing spring block 3. Plural edge bearing springs 5 are provided at a terminal plate 4 for forming voltage side pole edge bearing spring block 6. The ground side pole edge bearing spring block 3 and the voltage side pole edge bearing spring block 6 are disposed in parallel to each other facing the respective edge bearing springs 2, 5 each other, and they are contained in an inner shell 7 formed of thermosetting resin. Plural edge bearing springs 9 a provided at a terminal plate 8 for forming a ground edge bearing spring block 10. The edge bearing springs 9 of the ground edge bearing spring block 10 are put to face the edge bearing springs 2, 5 of the ground side pole edge bearing spring block 3 and the voltage side pole edge bearing spring block 6, and they are inserted into the inner shell 7. The inner shell 7 and the ground edge bearing spring block 10 are covered with an outer shell 11 formed of thermoplastic resin.