Abstract: A letter approval item including an approval document is created in an approval requester's PC and the approval document includes a signable region. An approval is requested by transmitting the letter approval item to a database server. A mobile-based approval item including the letter approval item is provided to a web/application server and then to an approver's mobile device when the approver's mobile device requests. The approval of the letter approval item is performed in the approver's mobile device in response to a direct signature of an approver. A signature image is created in the approver's mobile device by the direct signature of the approver. The signature image is transmitted to the web/application server and a final approval document is generated in the web/application server by inserting the signature image in the signable region of the approval document.