To provide a bottom part having more closeness in comparison with such conventional processing method as to need to process on site, to need to process by using a special device or to limit to short the processing time, etc., and exchangable only to damage portion and long service life.

a bottom block is constituted of one or more of precast blocks and one or more of precast blocks arranging molten metal hitting part formed so that the central part becomes high and the central peripheral part becomes low, or the one side end is formed at higher than or as the same height as the other side end, and refractories filled up between the above precast blocks or in the gap between the above precast block and the precast block arranging the molten metal hitting part. The molten metal hitting part is unitedly formed by using the same material as the precast block. Further, the molten metal hitting part is formed by using one or more pieces of bricks.