To provide a rotating motor system that can control to flow currents of both positive and negative directions to a field winding, and has a simple configuration.SOLUTION: A rotating motor system 10 includes: a rotating motor 30 including a field winding 34; a battery group 16 in which a first battery 15a and a second battery 15b are connected in series; a pair of busbars 28a and 28b to which a voltage of the battery group 16 is applied; a field converter 24 that is connected between the busbars 28a and 28b and allows current to flow to the field winding 34; and a control device 12 for controlling the field converter 24. The field converter 24 includes an arm A1 connected between the busbars 28a and 28b, the arm A1 consists of two switching elements S1 and S2 controlled by the control device 12 connected in series, one end of the field winding 34 is connected to ap between the two switching elements S1 and S2 of the arm A1 of the field converter 24, and the other end of the field winding 34 is connected to bp between the first battery 15a and the second battery 15b.SELECTED DRAWING: Figure 1