To provide a high silicon steel sheet which has little core loss by siliconizing treatment, and has excellent workability in punching.

The part requiring workability in a low silicon steel sheet 1 formed into a thin sheet by a rolling mill 3 from a continuous casting machine 2 is subjected to surface treatment for heat resistance such as the application of boron nitride by a surface treatment apparatus 4. This steel sheet is fed to a siliconizing treatment apparatus 5. SiC 114 is charged to the inside of a nonoxidizing gas atmosphere, and heating is performed to diffuse Si. The part subjected to the surface treatment is left as a low silicon part since siliconizing therein is disturbed, and working can satisfactorily be performed thereto.