PURPOSE: To provide a core for a deflecting yoke and its manufacturing method so as to eliminate the burr and the edge of divided surfaces in the vicinity of an end part of small diameter of a divided groove.

CONSTITUTION: In a core 1 for an approximately cylindrical deflecting yoke where the core is expanded from an end part 7 of small diameter toward an end part 8 of large diameter, a divided groove provided in an axial direction of an inner circumferential surface 2 and an outer circumferential surface 3 and a recessed part 9 provided at the connecting part of the inner circumferential surface 2 to the end surface 7A of small diameter in the vicinity of the end part 7 of small diameter of the divided groove provided in the inner circumferential surface 2 are provided. In the manufacturing method of the core for the deflecting yoke, an upper die having a blade for the divided groove to form the divided groove provided in the inner circumferential surface 2 of the core 1 for the deflecting yoke, and a lower die provided with a projecting part to form the recessed part 9 of the core for the deflecting yoke and a slide groove where the dividing blades of the upper die slide and are fitted to this projecting part are used in the forming process.