To improve accuracy in the workload estimation of a project.

Concerning the workload estimation supporting device for supporting the estimation of workload required for executing a project, this device is provided with a workload estimate information input means 3 for inputting workload estimate information required for estimating the workload of the project, workload estimating means 6 for estimating the workload on the basis of the inputted workload estimate information, workload result information input means 8 for inputting the workload result information of respective projects, error analytic means 14 for analyzing an error between the workload estimate information estimated by the workload estimating means and the workload result information inputted by the workload result information input means, and error cause input means 16 for inputting an error cause estimated to the error analyzed result of this error analytic means.