In this paper, the approximate equivalent circuit of the grooved solid pole synchronous motor is derived. In the approximate equivalent circuit, the upper part (grooved part) and the lower part (core part) of the grooved solid pole synchronous motor are separated. As the presence of the grooves on solid poles causes a part of the eddy current which is considered as an end effect problem, strictly theoretical solution of this problem is extremely difficult. In this paper, measured value of surface loss is described and studied by considering the end effect, and the surface loss reduction factor is also obtained. This grooving technique is used for the solid pole synchronous motor and for the claw pole machine.