To obtain a board resembling natural tortoiseshell in terms of skin touch and processability, thus useful as an alternative to natural tortoiseshell, by drying tortoiseshell 5K protein having a specific amino acid sequence and making it into powder which is then mixed with extrapure water followed by putting the mixture into a mold and conducting a hot-press molding.

First, tortoiseshell 5K protein manifested from a structural gene coding a protein having an amino acid sequence of the formula is dried and made into powder. Secondly, 12-15g of extrapure water is mixed with 100g of the powder, and 0.5-5wt.% of the mixture is homogeneously blended with 99.5-95wt.% of extrapure water-containing casein protein. Thereafter, the resultant blend is put into a mold and hot-pressed at 100-150°C under a pressure of 200-300kg/cm2 for a rather short time of 5-20min and then cooling thus affording the objective board for tortoiseshell material.