A rotating electric machine is provided, where a generator has an increased capacity and a reduced size achieved by electromagnetically effectively utilizing that parts of a rotor core which are outside the narrowest parts of magnetic poles of the rotor core to permit large field current and suppress an increase in temperature of rotor coils. The rotating electric machine includes a stator constructed by winding armature coils around a stator core (1), and a hollow circular cylindrical rotor. The rotor has at least one pair of magnetic poles (2), non-polar portions (3) between the magnetic poles, and interpolar portions (6) arranged in the non-polar portions. In the non-polar portions (3), a plurality of rotor slots (4) are arranged at predetermined intervals. Field windings are wound in each rotor slot (4). The cross-sectional areas (S) of the rotor slots (4) other than the rotor slots (4a) nearest to the magnetic poles (2) are gradually increased in the direction from the magnetic poles (2) to the interpolar portions (6).