To satisfy all of design properties, sound absorption, and executability and to assure a strength of a surface layer by forming a specific pattern layer of a surface layer of a mineral base plate and a laminated coating film layer, and forming the film layer of a reinforced coating film layer of a paint having higher viscosity than paint for forming an overcoating film layer.

As a mineral base plate 1, a rock wool plate is used. A pattern layer 11 made of an embossed pattern 11a and a travertine pattern 11b is formed on its surface layer of the plate 1, and the surface is covered with a laminated coating film layer 12. The pattern 11 is constituted of a protrusion and recess pattern in which strips are continued, the pattern 11b is superposed on an area executed with the pattern 11a, and constituted of pinhole patterns 11b1 sprinkled in irregular diameters, depths and densities and scraping recess patterns 11b2 discontinuously dispersed in irregular sizes, shapes and depths. The layer 12 is constituted of an overcoating layer of an aqueous paint having low viscosity and provided on the layer 11 and a reinforced coating film layer formed of an aqueous paint having a relatively high viscosity and coating mainly on the protrusion part of the pattern 11a from above.