This study focuses on improving the performance of a newly developed submerged impulse turbine suitable for small hydropower generation in drinking water pipelines. The turbine performance becomes lower for submerged operation due to disk friction on the runner surface and mixing loss by runner blades. Previous research revealed that a pair of a disk placed on both sides of the runner can suppress these losses. But, the turbine performance with torque loss suppression disks is not clarified. Therefore, the authors proposed a nozzle disk that integrates a disk and nozzles and examined the disk's effect on turbine performance. The nozzle disk is placed on the runner inlet side and supplies a jet to the runner. The disk shows a higher torque loss reduction for smaller clearance between the runner and disk. Moreover, the disk can generate multiple water jets with less velocity decay and keep an appropriate jet angle. As a result, the turbine with the nozzle disk shows higher efficiency than the previous research on the submerged impulse turbine.