The present invention can realize easy transition from a task managed by a To-Do list to a workflow. When an unprocessed task stored in the To-Do list database is converted by an instruction into the workflow in the client software, a document management system of the present invention extracts a workflow definition including an activity corresponding to an unprocessed task to be converted by the instruction and notifies a client software of the workflow definition. When the client software selects the workflow definition, server software creates an instance of the workflow corresponding to the selected workflow definition, and applies information about the task to be converted, to the activity corresponding to the task to be converted in the instance of the workflow.