PURPOSE: To easily change a driving number by constituting this system so that a user can set arbitrarily the driving number with an allocation switching device provided between a computer and plural memory drives.

CONSTITUTION: An allocation setting circuit 2 sets the allocation of a memory drive by a user. In accordance with the allocation, the allocation setting circuit 2 outputs an allocation instructing signal 4. The allocation instructing signal 4 is inputted to a DS signal converting circuit 3, and in accordance with the signal 4, a drive selecting signal 5 inputted from a computer 7 is converted and outputted as a converted drive selection signal 6, and inputted to memory drives 8 - 11. On the other hand, in the case a signal DSIA to a signal DS4A of the converted drive selection signal 6 are activated, respectively, each of the memory drives 8 - 11 is driven in accordance with the sequence.