According to one embodiment, there is provided a switching element driving power supply circuit that converts a main circuit voltage into a driving voltage of power-converting switching elements. The circuit includes a plurality of insulating power supplies, and a plurality of switching element driving power supply units. The insulating power supplies have respective direct-current input circuit ends connected in series, respective input-side circuits and output-side circuits insulated from each other, and respective output circuit ends connected in parallel. The power supply units are connected in parallel with the output circuit ends, and supplying power to the gate driving circuits of the power conversion switching elements.