PURPOSE: To shorten the maximum seeking distance and to shorten an access time by dividing a cylinder area of each of N pieces of disk devices into (n) equal parts and giving accesses to these divided (n) areas as a single disk device.

CONSTITUTION: A drive/cylinder number receiving part 2 receives the drive and cylinder numbers that received the access requests from a CPU 1. A drive/ cylinder number converting part 3 converts the drive and cylinder numbers received by the part 2 based on the definition of conversion. A head control part 4 performs the simultaneous seeking actions for three disk devices 5W7.