Provided is an automatic compensation device including a seller terminal supplying a service and a purchaser terminal purchasing the service, which are connected to each other via a communication network. In more detail, the automatic compensation device calculates a compensation to be provided to a purchaser by using the service evaluation information about a purchased service of the purchaser and the previously-stored purchase credit information about the purchaser, then updates the purchase credit information of the purchaser according to the compensation, and differentially paying an installment to the service supplier according to the compensation.