A driving system comprising: a pantograph that collects single-phase AC power from an overhead contact line connected to a single-phase AC power supply, a main transformer that steps down the collected single-phase AC power, two wires being arranged on the low voltage side of the main transformer, a power generation unit that comprises an engine and a three-phase AC power generator to output three-phase AC power, a first power conversion device (21, 22) that converts AC power to DC power, a second power conversion device that drives an electric motor by using the DC power converted by the first power conversion device as a power supply, and switching means (12, 13) configured to selectively electrically connect an AC side of the first power conversion device to one of a wire on a low voltage side of the main transformer that supplies a single-phase alternating current, and an output of the power generation unit that supplies a three-phase alternating current, wherein: the first power conversion device performs an operation of converting the AC power connected by the switching means to DC power according to the number of phases of the AC power; the first power conversion device comprises power conversion circuits for four phases comprising two circuits connected in series, the connected circuits comprising semiconductor elements with self-extinction capability and diodes connected in antiparallel, two phases of the power conversion circuits being connected to one of the wires on the low voltage side of the main transformer through the switching means, the other two phases of the power conversion circuits being connected to the other of the wires on the low voltage side of the main transformer through the switching means, and the first power conversion device being connected to the three-phase AC power supply through three phases of the power conversion circuits, the switching means connects the two wires on the low voltage side of the main transformer to the power conversion circuits for four phases to supply single-phase AC power to the first power conversion device when a vehicle travels on an overhead contact line installation route, and the switching means connects a three-phase AC output of the power generation unit to the power conversion circuits for three phases to supply three-phase AC power output from the power generation unit to the first power conversion device when the vehicle travels on a route without an overhead contact line or on an overhead contact line route in an abnormal state. a pantograph that collects single-phase AC power from an overhead contact line connected to a single-phase AC power supply, a main transformer that steps down the collected single-phase AC power, two wires being arranged on the low voltage side of the main transformer, a power generation unit that comprises an engine and a three-phase AC power generator to output three-phase AC power, a first power conversion device (21, 22) that converts AC power to DC power, a second power conversion device that drives an electric motor by using the DC power converted by the first power conversion device as a power supply, and switching means (12, 13) configured to selectively electrically connect an AC side of the first power conversion device to one of a wire on a low voltage side of the main transformer that supplies a single-phase alternating current, and an output of the power generation unit that supplies a three-phase alternating current, the first power conversion device performs an operation of converting the AC power connected by the switching means to DC power according to the number of phases of the AC power; the first power conversion device comprises power conversion circuits for four phases comprising two circuits connected in series, the connected circuits comprising semiconductor elements with self-extinction capability and diodes connected in antiparallel, two phases of the power conversion circuits being connected to one of the wires on the low voltage side of the main transformer through the switching means, the other two phases of the power conversion circuits being connected to the other of the wires on the low voltage side of the main transformer through the switching means, and the first power conversion device being connected to the three-phase AC power supply through three phases of the power conversion circuits, the switching means connects the two wires on the low voltage side of the main transformer to the power conversion circuits for four phases to supply single-phase AC power to the first power conversion device when a vehicle travels on an overhead contact line installation route, and the switching means connects a three-phase AC output of the power generation unit to the power conversion circuits for three phases to supply three-phase AC power output from the power generation unit to the first power conversion device when the vehicle travels on a route without an overhead contact line or on an overhead contact line route in an abnormal state.