On public constructions, that the first planed projects delay than the scheduled completion day occurrence frequently because gap between the scheduled construction durations and the actual construction durations. These facts connect with not only problems of the construction during as the construction delay but also brought about the distribution costs increase as the failure of facility use plan and the people discomfort weight, failure of the production and the supply using facility then tremendous loss of each part etc. For reduce these loss, it must improve accuracy of the scheduled construction duration estimating when it order. This study try contribute to a successful manage of public project and reduce the construction duration extension frequent of the construction during, and then ensure the suitable construction duration by present the estimation model of the scheduled construction duration that include the construction duration correct element using as an index on the scheduled construction duration estimation.