A rolling stock system, comprising: an AC electric rolling stock; and a detector configured to detect a voltage of an overhead wire; wherein the AC electric rolling stock includes; a main transformer equipped in a base rolling stock; a power collector for obtaining an AC power from the overhead wire connectable to a primary winding of the main transformer; a first circuit connected to a secondary winding (112a, 112b) of the main transformer, the first circuit having a first AC-DC power converter for converting an alternate current of the overhead wire to a direct current and for performing a regeneration operation returning energy from the DC side to the AC side, the first circuit being a drive power conversion circuit for driving a rolling stock driving motor; a second circuit connected to a tertiary winding of the main transformer, the second circuit having a second AC-DC power converter performing a regeneration operation as the first AC-DC power converter of the drive power conversion circuit; a power storage device connected to one or more of the AC-DC power converters that are included in the first and second circuit connected to the secondary winding (112a, 112b) or the tertiary winding of the main transformer; wherein the detector is configured to detect the voltage of the overhead wire while the power collector is not connected to the primary winding; wherein the rolling stock system is configured to drive the at least one of the one or more AC-DC power converters connected to the power storage device to apply energy of the power storage device to the secondary winding (112a, 112b) or the tertiary winding of the main transformer, and to reversely excite the main transformer such that the primary side of the main transformer has the same phase and same voltage as the detected voltage of the overhead wire, and wherein the rolling stock system is configured to subsequently connect the overhead wire and the primary winding of the main transformer to each other by the power collector such that electric power is supplied from the overhead wire to the main transformer through the power collector. an AC electric rolling stock; and a detector configured to detect a voltage of an overhead wire; wherein the AC electric rolling stock includes; a main transformer equipped in a base rolling stock; a power collector for obtaining an AC power from the overhead wire connectable to a primary winding of the main transformer; a first circuit connected to a secondary winding (112a, 112b) of the main transformer, the first circuit having a first AC-DC power converter for converting an alternate current of the overhead wire to a direct current and for performing a regeneration operation returning energy from the DC side to the AC side, the first circuit being a drive power conversion circuit for driving a rolling stock driving motor; a second circuit connected to a tertiary winding of the main transformer, the second circuit having a second AC-DC power converter performing a regeneration operation as the first AC-DC power converter of the drive power conversion circuit; a power storage device connected to one or more of the AC-DC power converters that are included in the first and second circuit connected to the secondary winding (112a, 112b) or the tertiary winding of the main transformer; wherein the detector is configured to detect the voltage of the overhead wire while the power collector is not connected to the primary winding; wherein the rolling stock system is configured to drive the at least one of the one or more AC-DC power converters connected to the power storage device to apply energy of the power storage device to the secondary winding (112a, 112b) or the tertiary winding of the main transformer, and to reversely excite the main transformer such that the primary side of the main transformer has the same phase and same voltage as the detected voltage of the overhead wire, and wherein the rolling stock system is configured to subsequently connect the overhead wire and the primary winding of the main transformer to each other by the power collector such that electric power is supplied from the overhead wire to the main transformer through the power collector.