To provide a tool capable of easily forming dimples even on existing paddles and oars, optionally determining the shape and the mounting position of the dimples and forming a rowing oar such as an oar, a paddle optimal for an operator.

One or more penetrated holes are formed on a base material or a recess is formed on its surface side, and one side of the base material where the penetrated holes are bored, or the rear surface of the one provided with the recess forms an adhesive face. Dimples are formed on a paddle blade surface of the rowing oar by sticking the adhesive face to the paddle blade surface.