To provide a pre-nozzle for a drive system of a water craft for further improving drive efficiency of a Low-speed large-capacity ship.

A propeller-less pre-nozzle 10a of a drive system for a water craft, comprises: a water inlet aperture; and a water outlet aperture. In the water inlet aperture and the water outlet aperture, fin systems 14a to 14e are installed. In inlet regions of the water inlet aperture and the water outlet aperture, the fin systems 14a to 14e are not included. In the propeller-less pre-nozzle 10a, the pre-nozzle 10a is configured in rotary asymmetry so as to further improve drive efficiency.