To restrict the use of expensive titanium alloy only to a fluid contact part for reduction in material cost, in a submergible motor pump with an impeller mounted on the spindle of a submergible motor, by jointing a motor side part to a pump side part, each of which is formed out of different material, by means of shrink-fit for forming a spindle.

This low-power submergible seawater pump, used as a bilge pump for a fishing boat, is formed out of a pump part P and a motor part M as one body with a pump impeller 3 mounted at the front end of the spindle 2 of the motor. The motor side part 21 and the pump side part 22 of the spindle 2 are formed out of different material respectively. The motor side part 21 is constituted of a magnetic material such as carbon steel and stainless alloy for full performance of the motor part M, and the pump side part 22 is constituted of titanium alloy in consideration of corrosion resistance to seawater. A projecting shrink fit end 21a is formed at the motor side part 21, and a recessed shrink fit end 22a is formed at the pump side part 22, thereby jointing them by means of shrink fit at a joining part 23.