To restrain a contact at a spiral section of a filament when using the spiral filament.

In an electrode mount 3 where the filament 32 is connected to first and second leads 31a, 31b, the first and second leads 31a, 31b respectively have first and second flat sections 311a, 311b, and the filament 32 has first and second leg sections 321a, 321b, and the spiral section 322 connected to the first and second sections 321a, 321b. The first leg section 321a is connected to the first flat section 311a, and the second leg section 321b is connected to the second section 311b. When the center of the spiral section 322 is set up to be O, the first leg section 321a and the second leg section 321b are arranged so as to be approximate point-symmetry to the center O.