The Shiga Prefectural Government (SPG) is in a process of reviewing and revising 'Mather Lake 21 Plan', which is a comprehensive conservation plan developed in 2000 for Lake Biwa. This study was meant to compass the values of people for Lake Biwa, allowing them to be reflected in the revised plan. The authors first conducted a value survey (VS) as a part of an opinion survey by the SPG, requesting prefectural inhabitants to evaluate the level of importance of five major functions of the lake in absolute terms. The five major functions include the following: water resources, ecosystem, landscape, lifestyle and industry. An experiment involving undergraduate students also was conducted, in which the students were asked to evaluate the level of importance, in both absolute and relative terms. Relative evaluations were accomplished by the Analytic Hierarchy Process method. The results indicated that (i) The average values of the prefectural people regarding Lake Biwa, in terms of the lake's functions, were determined, with the values found to be less subject to people's attributes; (ii) A good linear relationship between the absolute and relative evaluations was obtained in the student experiment, suggesting that the absolute evaluations could be converted to relative ones with the derived relationship; and (iii) By converting the absolute evaluations of the VS to relative ones, it was revealed that prefectural residents attached importance to the lake's functions, with the relative order of importance being water resources, ecosystem, landscape, industry and lifestyle.