1. A pass/fail judgment device comprising: a discriminant function computing unit for computing discriminant functions which give variables used to separate the frequency distributions of pass category and fail category from a plurality of pieces of parameter information which make pass/fail judgment factors and pass/fail judgment result information thereof; a statistical parameter computing unit for computing the center of distribution and distribution parameters indicating the breadth of the distribution for said variables with respect to either or both of said pass category and fail category; a threshold determining unit for taking as a threshold for pass/fail judgment the value of said variable which gives a specific distribution probability in either or both of said categories based on said center of distribution and distribution parameters; a parameter information acquiring unit for acquiring a plurality of pieces of parameter information on pass/fail judgment objects; and a pass/fail judging unit for comparing the value of said variable obtained by substituting the parameter information into said discriminant function with said threshold and thereby makes pass/fail judgment.