To reduce or eliminate the resistance of water to enhance the performance of a pump by disposing first and second impellers respectively in the middle and rear of a casing, providing a second impeller shaft inside a first impeller hollow shaft, and rotating the impellers in opposite directions.

A casing member 13 is provided with a forward impeller 61 including a central hub 63 and a rearward impeller 81 including a central hub 83 and is further provided with a rearward hub 101 and a plurality of vanes 103. The forward impeller 61 includes a hollow outer forward impeller drive shaft 123 and a bevel gear 125 is provided at the front end thereof. The inner rearward impeller drive shaft 133 of the rearward impeller 81 extends into the hollow of the impeller drive shaft 123 and is provided with a bevel gear 135 at its front end. The bevel gears 125, 135 mesh with a bevel gear 143 at the end of a drive shaft 141 and rotate in opposite directions. Thus, the second impeller 81 adds energy to water straightened through the vanes to enhance performance.