PURPOSE: To reduce weight of a magnetic ballast adopted for illumination or the like in cuttlefish angling fishery.

CONSTITUTION: An active filter 1 and an inverter 2 are connected in order to commercial electric power supply or a ship's generator. An output frequency of the inverter 2 is taken from an intermediate frequency of 290Hz to 500Hz, and output voltage is taken from lighting stating voltage of a metal halide lamp or a fluorescent lamp. The active filter 1 is composed of a coil or the like or an active filter control circuit, and keeps output voltage and an electric current of the inverter 2 in the same phase. Thereby, a magnetic ballast is reduced in weight to about 1/4, and a loss of the ballast is minimized, and the occurrence of a higher harmonic wave noise is completely eliminated due to the intermediate frequency.