A gate-power-supply device comprising: - a DC power supply ; - an inverter circuit for converting DC power from the DC power supply into high-frequency power and for outputting the high-frequency power; - a transformer composed of a primary-side coil supplied with the high-frequency power, and a plurality of secondary-side coils wound around transformer cores through which the primary-side coil passes; - a plurality of rectifier circuits for respectively rectifying high-frequency powers outputted from the respective secondary-side coils of the transformer, the plurality of rectifier circuits being adapted for respectively driving gate drivers for a plurality of semiconductor switching devices , by outputs from the rectifier circuits ; - a plurality of secondary-side parallel capacitors (C P ) connected in parallel to the respective secondary-side coils , the plurality of secondary-side parallel capacitors (C P ) being adapted for canceling inductance components of the secondary-side coils at drive frequency of the inverter circuit ; - a primary-side series capacitor (C S ) connected in series to the primary-side coil , the primary-side series capacitor (C S ) being adapted for canceling an imaginary term (inductance component) of a combined impedance of the gate drivers , the rectifier circuits , the secondary-side parallel capacitors (C P ), the secondary-side coils , the transformer cores , and the primary-side coil , which are a load viewed from the inverter circuit ; and - a sequential power transfer section which is provided between the transformer and the plurality of rectifier circuits to sequentially transfer power supplied via the secondary-side coils of the transformer to the plurality of rectifier circuits , wherein the gate drivers for the plurality of semiconductor switching devices are respectively driven via the sequential power transfer section and the plurality of rectifier circuits , wherein the transformer cores are formed in an arc shape having an opening. - a DC power supply ; - an inverter circuit for converting DC power from the DC power supply into high-frequency power and for outputting the high-frequency power; - a transformer composed of a primary-side coil supplied with the high-frequency power, and a plurality of secondary-side coils wound around transformer cores through which the primary-side coil passes; - a plurality of rectifier circuits for respectively rectifying high-frequency powers outputted from the respective secondary-side coils of the transformer, the plurality of rectifier circuits being adapted for respectively driving gate drivers for a plurality of semiconductor switching devices , by outputs from the rectifier circuits ; - a plurality of secondary-side parallel capacitors (C P ) connected in parallel to the respective secondary-side coils , the plurality of secondary-side parallel capacitors (C P ) being adapted for canceling inductance components of the secondary-side coils at drive frequency of the inverter circuit ; - a primary-side series capacitor (C S ) connected in series to the primary-side coil , the primary-side series capacitor (C S ) being adapted for canceling an imaginary term (inductance component) of a combined impedance of the gate drivers , the rectifier circuits , the secondary-side parallel capacitors (C P ), the secondary-side coils , the transformer cores , and the primary-side coil , which are a load viewed from the inverter circuit ; and - a sequential power transfer section which is provided between the transformer and the plurality of rectifier circuits to sequentially transfer power supplied via the secondary-side coils of the transformer to the plurality of rectifier circuits , <EOS>