The frame member 11 is provided with base portions 12 and male thread portions 13 that project upward from the base portions 12 (see FIG. 2 and the like). Through-holes through which the male thread portions 13 can pass are formed in the leading end portions 422b of the extension portions 422 of the conductive member 42. By inserting the male thread portions 13 into the through-holes formed in the leading end portions 422b, passing the male thread portions 13 through through-holes formed in terminals 51 of the connection members 50, and screwing nuts or the like onto the male thread portions 13, the leading end portions 422b and the terminals 51 are pressed against the base portions 12 and brought into close contact with each other. Accordingly, the conductive member 42 and the connection members 50 are put into an electrically connected state (see FIG. 5 and the like).