PURPOSE: To enhance the efficiency of a write/read processing operation by a method wherein the following are started at the same time: the retreat action of an accessor mechanism part on one side; and the recording-medium conveyance action of an accessor mechanism part on the other side.

CONSTITUTION: A DIR control part 19 judges the movement range of an accessor (ACC) mechanism part 1 from the address (e.g. a cell 11) of a designated movement source and from the address (e.g. MTU 9) of a movement destination by means of a move instruction from a host device. Then, it sends out a move instruction to an accessor control part 20. When an ACC mechanism 2 exists within the movement range of the mechanism part 1, it instructs the conveyance action of the mechanism part 1 and, at the same time, instructs the retreat of the mechanism part 2 to an accessor mechanism control part 23. The control part 20 performs an operation, computes a safe distance and retreats the mechanism part 2 via the AMC 23.