A mashup method is disclosed. The Web APIs which the Web application uses are specified by analyzing descriptions of drivers used to access the multiple Web APIs from a Web application to external devices. A Web Application Programing Interface list is created to indicate the Web APIs. The Web application is analyzed. The external devices including the Web APIs which the Web application accesses are estimated. An external device list which indicates the estimated external devices is created. By referring to the external device list, when one or more external devices do not exist, an access to each of the Web APIs pertinent to the Web application is restricted where the one or more external devices include the Web APIs used in a process of the Web application and the process is realized by mashup.