Abstract: In a sharing forecast system for forming a forecast by sharing two companies, upon accidentally matching forecast values formed based on different factors by transaction companies, a difference on estimation is found and it can easily be specified, and the forecast values can easily be corrected. Two companies share both a forecast value and basis information obtained by patterning a factor for calculating the forecast value. Upon satisfying criteria that the basis information of the two companies does not match each other, it is determined that there is a different estimation of the forecast value. In the case of the determination, the basis information is presented to the two companies, a recommended value for correcting the forecast value is calculated based on the basis information, and the calculated value is presented to the two companies.