PURPOSE: To prevent a partition wall from cracking or deforming, also reduce air gaps, and improve motor efficiency, pump efficiency, and the life of a motor.

CONSTITUTION: One of two chambers partitioned with a partition wall 27 is set to be a motor chamber 21, and the other is set to be a pump chamber 28 to which cooling water L is fed. In the motor chamber 21, a plurality of cores 23 wound with stator coils 25 are radially arranged. In the pump chamber 28, an impeller 30 rotationally movably held is arranged, in which rotor magnets 32 are arranged on the back so as to oppose to a plurality of the cores 23. The extreme end 23a of each core 23 fittingly penetrates the partition wall 27 and exposed to the pump chamber 28.