Small hydropower development is one of the best way for enhancement of energy security and good solution of global environmental issues. A new submerged impulse turbine has been developping for generation by replacing pressure reducing valve in drinking water pipe lines. This study is especially focused on torque loss on the turbine, but it is not fully understood the reason why the loss is occurred. The torque loss is serious problem for a submerged turbine performance. Thus the torque loss on the runner and a disk was measured, and flow visualization by oil film method was conducted. As a result, the trque loss on the runner becomes four times larger than that on a disk. It is revealed that the flow field near the surface on a disk is a little different from that on the disk, and impinging water flow on the suction side of blade enhances the torque loss on the runner.