An insulator is provided between a stator core and a conductive wire provided on the stator core. The insulator includes a wound portion, around which the conductive wire is wounded, having a substantially rectangular shape; and a flange, formed in the axial end of the wound portion in the stator tooth tip side, for pressing the conductive wire in the axial direction (radial direction relative to the rotation axis of a rotor in a configuration of a rotating electrical machine). The flange includes four corner portions at its four corners, and intermediate portions formed between the four corner portions to have a width (B2) narrower than the width (B1) of the four corner portions. In addition, the flange has a tip with a curved shape.