PURPOSE: To reduce the size of a motor by a method wherein holes are formed in the outer circumferential part of an armature core composed of the later-built structure of thin plates and hollow pipes are inserted into the holes and expanded so as to be unified with the armature core.

CONSTITUTION: Slots 3 are provided in the inner circumferential part of an armature core 2 composed of the layer-built structure of thin plates and windings 4 are inserted into the slots 3. A plurality of holes 5 are formed in the outer circumferential part of the armature core 2. Hollow pipes 6 are inserted into the holes 5 and both the end parts of the pipes 6 are expanded at both the end parts of the armature core 2 or the pipes 6 are expanded by a pressure applied to the inside of the pipes 6 to unify the pipes 6 with the armature core 2. Further, the pipes 6 are connected to each other successively with connection pipes 7 to form a passage 8. Coolant is made to flow through the connected pipes 6 to discharge the heat generated by the windings for cooling. With this constitution, a rotating electric machine which has a simple construction and an economical and small cooling structure can be obtained.