PURPOSE: To improve the throughput of the system and the efficiency of use by temporarily storing data in a secondary storing means and afterwards, storing the data in an optical disk medium again in a batch manner.

CONSTITUTION: When a data write request to an optical disk medium 5m is generated from a second information processor, a system control part 9 dispatches the data to a data I/O part 10, and the I/O part 10 stores the data in a magnetic disk device 11 after adding the medium name 5m to be originally stored. Afterwards, the control part 9 reads the data stored in the device 11 by using the medium name and executes the mount request of the medium 5m. An integrated optical disk control part 8 takes out the medium 5m from a storage shelf 4 by using a medium exchange arm 7, mounts it to an optical disk drive 6 and writes the data transmitted from the control part 9 in the medium 5m.