PURPOSE: To increase thermal conduction of a stator coil by winding the stator coil on a metal spool of copper, etc., tightly, and fitting the copper spool in the outside duct closely.

CONSTITUTION: The expansion coefficient of materials of a stator coil 2, copper spool 9 and outside duct 4 is about the same. The copper spool 9 as a heat channel from the stator coil 2 as heat source through the outside duct 4 has large thermal conduction. Accordingly, temperature rise from the time of assembly to the time of operation and the difference in thermal expansion by temperature difference of each part are controlled by assembling these constructions 2, 9 and 4 in a state to adhere to each other, and the generation of gaps and stress among the constructions 2, 9 and 4 can be avoided.