1. A non-transitory computer-readable recording medium that stores therein a scale-parameter calculating program that causes a computer to implement a method comprising: calculating scale parameters, each of which is for use in normalization of a distribution of values of each of explanatory variables in calculation of inter-explanatory variable distances, to predict a value of a objective variable of an unknown case by extracting one or more known cases similar to the unknown case from known cases based on inter-case distances, the inter-case distances being obtained based on the inter-explanatory distances, each of the inter-explanatory variable distances being a distance between each of the known cases and the unknown case taken for each of explanatory variables, each of the cases including the explanatory variables each expressed by a numerical value and the objective variable expressed by a character string, each of the known cases being a case that has a known objective variable value, the unknown case being a case that has an unknown objective variable value; calculating each of the scale parameters for each of the explanatory variables of a union set combined by a known case set of the known cases and an unknown case set of the unknown case; and holding by storing the scale parameters each of which is calculated for each of the explanatory variables in the calculating, wherein an unknown case is sequentially extracted from the unknown case set as a prediction target, and the scale parameter of a union set combined by the unknown case and the known case set is calculated for each of the explanatory variables.