A mashup method for realizing a process function by accessing multiple Web Application Programming Interfaces (61a, 62a), comprising: identifying, by a computer, Web Application Programing Interfaces (61a, 62a) which a first Web application uses, by analyzing descriptions of drivers used to access the Web Application Programing Interfaces (61a, 62a) from the first Web application to a first external device for acquiring and sending authentication information to the first Web application and to a second external device for conducting a predetermined process based on the authentication information; creating and storing, by the computer, a Web Application Programing Interface list which indicates the Web Application Programing Interfaces (61a, 62a) in a storage unit; analyzing, by the computer, the Web application and estimating the names of the first external device and the second external device including the Web Application Programing Interfaces (61a, 62a) which the first Web application accesses; creating and storing, by the computer, an external device list which indicates the estimated external first and second devices (61, 62) in the storage unit; and restricting, by the computer, an access to each of the Web Application Programing Interfaces (61a, 62a) pertinent to the first Web application by referring to the external device list, when at least the second external device is not available, the first and second external devices (61, 62) including the Web Application Programing Interfaces (61a, 62a) of the first external device and the second external device used in a first process of the first Web application, the first process realized by mashup. identifying, by a computer, Web Application Programing Interfaces (61a, 62a) which a first Web application uses, by analyzing descriptions of drivers used to access the Web Application Programing Interfaces (61a, 62a) from the first Web application to a first external device for acquiring and sending authentication information to the first Web application and to a second external device for conducting a predetermined process based on the authentication information; creating and storing, by the computer, a Web Application Programing Interface list which indicates the Web Application Programing Interfaces (61a, 62a) in a storage unit; analyzing, by the computer, the Web application and estimating the names of the first external device and the second external device including the Web Application Programing Interfaces (61a, 62a) which the first Web application accesses; creating and storing, by the computer, an external device list which indicates the estimated external first and second devices (61, 62) in the storage unit; and restricting, by the computer, an access to each of the Web Application Programing Interfaces (61a, 62a) pertinent to the first Web application by referring to the external device list, when at least the second external device is not available, the first and second external devices (61, 62) including the Web Application Programing Interfaces (61a, 62a) of the first external device and the second external device used in a first process of the first Web application, the first process realized by mashup.