PURPOSE: To economically manufacture the shadow mask frame structure with high mechanical strength by hardening the skirt and flange sections which are bent and formed on the edge of the effective section.

CONSTITUTION: The shadow mask frame structure 21 consists of the effective section 25 which is composed of the hole section whose opening sections 22 are perforated regularly and non-hole section 24 on its peripherary, the skirt section 26 formed by bending and molding the edge of the effective section 25, and the flange section 27. Hardening is applied from almost the central part (shown by dashed lines) of the skirt section 26 to the flunge 27. This hardening is performed by the chemical hardening method by which the tip section (shown in the arrow 29) from the central part 28 of the skirt 26 is inserted into a carbonized box and by the physical hardening method by which the tip section from the central part of the skirt 26 is high-frequency-heated and is then quenched.