A software distribution system for sewing machine includes a server and a sewing machine. The server generates authentication key data dedicated for a sewing machine only upon initial transmission of medium identification data and sewing machine identification data from a terminal and stores the authentication key data in mapping with the medium identification data. If a valid medium identification data and an invalid sewing machine identification data are thereafter transmitted to the server, the stored data is not updated and the authentication key data is transmitted to the terminal. If determined that a control program transmitted from the terminal is not free of charge based on a version information thereof, calculated identification data corresponding to the sewing machine identification data is generated based on the authentication key data transmitted from the server, whereupon successful verification of calculated identification data with the sewing machine identification data, the control program is invoked.