To provide a jet propulsion machine for water vehicle for suppressing degradation of the engine output by reducing resistance losses in a jet water passage, and increasing the propulsive force by preventing generation of turbulent flow.

This jet propulsion machine 1 for water vehicle comprises a drive shaft 2 connected to an engine, an impeller 3 comprising a boss 18 fitted to an end part of the drive shaft 2 and a plurality of blades fixed to the boss 18, and a jet water passage 10 formed between a water intake 9 on a water vehicle bottom side and a water injection nozzle 5 on a stern side, has a prismatic part 16 for tool hook of a polygonal outline shape on the boss 18, and further comprises a cap 17 to cover the prismatic part.