In this paper, a self-rotating waterjet nozzle system that has a vane pump for braking rotational speed of nozzle system was proposed, and a prototype of a nozzle system was developed. The nozzle system consists of a conventional self-rotating nozzle system and a vane-pump type brake system. To clarify the effect of choke valves, which were situated in the flow line between the discharge and suction ports of the vane pump, on the relation between the rotational torque and the rotational speed of nozzle system, a measurement of the rotational speed of nozzle system was conducted. The main results obtained in this study can be summarized as follows: The rotational speed of nozzle system obtained for the nozzle system with the vane-pump type brake system was much smaller than that obtained for the nozzle system without the brake system. In addition, the rotational speed of the nozzle system was decreased with decreasing the flow area of the choke valve. Accordingly, it is concluded that the developed vane-pump type brake system is effective for decreasing the rotational speed of the self-rotating nozzle system.