To facilitate winding and to prevent magnetic efficiency from decreasing by forming an annular core member by connecting a plurality of core pieces and an insulation connection member, and forming an inner slot opening.

The stator core structure, a stator core-winding method, and a rotation detector consist of an H-shaped core piece 20 where an annular core member 1 has a protrusion pole 3, and an insulation connection member 22 for connection each core piece 20, and an annular yoke member 12 is coaxially provided at the outer periphery of the annular core member 1.