PURPOSE: To provide a small stabilizer with stable characteristics even when a plurality of coils are incorporated in accordance with a plurality of discharge lamp.

CONSTITUTION: A core 11 has a side-leg core 12, a center-leg core 13, an end core 14, and a middle core 15. The center-leg core 13 has an air gap 16 for leakage flux. The core 11 has coil storing parts 17 for storing coils in a way that the magnetic flux generated from each coil increases mutually. Since the coils are mounted on the same core 11, the electric characteristics are stable even under an effect of magnetic interaction. In this constitution, the magnetic flux in each coil is increased mutually so that each coil requires fewer numbers of turns than a coil with a single-core structure. Since the flux of coils is cancelled mutually in each direction at the middle core 15 put among the coils, the cross suction of the middle cores 15 can be reduced.