PURPOSE: To provide indents continuously on steel sheet surface which is effective in decreasing iron loss by embedding or flame-spraying high hard materials on the roll surface to provide specified sized fine protrusions on the roll surface, making it possible to introduce fine strains on its surface.

CONSTITUTION: The apparatus comprises the roll on which lineary arranged fineprotrusions parallel to the direction of the roll are formed by embedding or spraying high hardness substances. Said fine protrusions are formed with the width of 50W1,000μm, 2W10μm in height, and with each interval of 2W20mm along with the perimeter of the roll body. The roll is located at the continuous line following cooling steps of flattening annealing process of the directional Si- steel strip. With this apparatus, the indents effective in decreasing iron loss are given continuously.