PURPOSE: To facilitate an assembly of the pump by a method wherein outer and inner casings of motor, pump casing etc. are formed by press formed steel plate and open end part of the inner casing of the motor is held between the outer casing of the motor and the motor casing.

CONSTITUTION: Outer casing 10 of the motor is formed such that a steel plate is drawn to form a cylindrical cup and a motor stater 14 is fixed to the inner circumference of the casing. In the casing 10 is inserted the motor inner casing 22 acting as a stator can and the rotor casing, the casing 22 is also drawn to form a cylindrical cup. In turn, the pump casing 12 is formed such that the suction port 26 is press drawn and drawn to form an entire substantial lid-shape. At the open edge is formed an outer flange 30 having the same diameter as that of the flange 16 of the casing 10. Between both flanges 16 and 30 is held an outer flange 24 of the inner casing 22 and then these flanges 16, 24, 30 are welded.