To provide a ballast for a discharge lamp having good thermal conductivity from a coil to a charging filler and having superior heat radiating characteristic.

A bump 31 and a projected part 3 are provided on an outer face of a brim part of a molded bobbin 1 which winds a coil 8. A U-shaped insulating board formed into a U-shape is mounted to the bump 31 and the projected part 3, and insulation between the surface of coil 8 and inside face of the core 7 is secured by the U-shaped insulating board 4. At least one part of the surface of coil 8 makes a direct contact with a charging filler.