Conventionally, it has been impossible to use a virtual tape volume having the same volume serial number and different media. A computer implemented virtual tape system enables making definition of a virtual tape volume of another medium with the same volume serial number and definition of a virtual tape magazine of grouped virtual tape in a virtual tape management table. A virtual tape control mounts a virtual tape volume of a virtual tape magazine used in a job or a virtual tape volume on a virtual tape device based on a management table correlating the job with the virtual tape magazine or a command.