To realize a totally-enclosed travelling-air cooling type main motor, etc., for a car emitting an output in the same extent by the same weight and frame dimensions as an open type dynamo-electric machine by improving cooling.

A ring-shaped cooling fin 2 is installed to a cylindrical frame 1, and both ends of the cooling fin 2 are closed by brackets 3. A motor is arranged so as to have the axial center of a horizontal shaft at a right angle in the progressive direction of a car progressing before and behind. A travelling- air guide 11 extended in the axial direction is installed along the lower section of the cooling fin 2. A clearance is formed between the travelling-air guide 11 and the cooling fin 2 at the lower end of the guide 11. A plurality of closing sections 11a and a plurality of adjacent opening sections 11b are formed near the upper end of the travelling-air guide 11, and the closing sections 11a and the opening sections 11b are formed alternately before and behind in the progressive direction of the car. Inverted V-shaped air guides 12 are formed to the brackets 3 extending over a front in the progressive direction of the car.