An electrical machine system comprising: - a first electrical machine; - a second electrical machine provided next to the first electrical machine; - an electric power converter; - and a shaft; - wherein each of the first electrical machine and the second electrical machine includes a stator (5, 7) having a winding and an iron core, a rotor (6, 8) having a winding and an iron core and disposed on the inner side of the stator (5, 7), and an outer periphery surrounded by a frame (15, 16), - wherein the rotor of the first electrical machine and the rotor of the second electrical machine are mechanically connected to the shaft, - wherein the stator of the second electrical machine has a smaller outer diameter than the stator of the first electrical machine has, - wherein the electric power converter is mechanically connected to the shaft and placed in the space on the inner side of the rotor of the first electrical machine, and is electrically connected to the winding of the rotor of the first electrical machine and the winding of the rotor of the second electrical machine, characterized in that it further comprises - an internal fan provided next to the second electrical machine, and - a heat exchanger; - wherein the internal fan is mechanically connected to the shaft and circulates internal air into the second electrical machine, the electric power converter, and the first electrical machine, and - wherein the heat exchanger is placed on the outer side of the second electrical machine, external air flowing into the heat exchanger and the internal air circulated by the internal fan flowing into the heat exchanger, and the heat exchanger cooling the entered internal air by heat exchange between the entered internal air and the entered external air. - a first electrical machine; - a second electrical machine provided next to the first electrical machine; - an electric power converter; - and a shaft; - wherein each of the first electrical machine and the second electrical machine includes a stator (5, 7) having a winding and an iron core, a rotor (6, 8) having a winding and an iron core and disposed on the inner side of the stator (5, 7), and an outer periphery surrounded by a frame (15, 16), - wherein the rotor of the first electrical machine and the rotor of the second electrical machine are mechanically connected to the shaft, - wherein the stator of the second electrical machine has a smaller outer diameter than the stator of the first electrical machine has, - wherein the electric power converter is mechanically connected to the shaft and placed in the space on the inner side of the rotor of the first electrical machine, and is electrically connected to the winding of the rotor of the first electrical machine and the winding of the rotor of the second electrical machine, characterized in that it further comprises - an internal fan provided next to the second electrical machine, and - a heat exchanger; - wherein the internal fan is mechanically connected to the shaft and circulates internal air into the second electrical machine, the electric power converter, and the first electrical machine, and - wherein the heat exchanger is placed on the outer side of the second electrical machine, external air flowing into the heat exchanger and the internal air circulated by the internal fan flowing into the heat exchanger, and the heat exchanger cooling the entered internal air by heat exchange between the entered internal air and the entered external air.