PURPOSE:To reduce the burden of a processor, and to prevent the generation of an error by confirming whether the release or the acquisition of a storage area is possible or not in a case of the control of the processing of the release or the acquisition of the storage area, etc. CONSTITUTION:After the processing of a command area 5 designated by a head pointer area 4 is completed by an auxiliary processor 2, the auxiliary processor 2 copies the information of the head pointer area 4 in a pointer copy area 7. Afterwards, the auxiliary processor 2 writes the information of a pointer area 6 in the head pointer area 4. Then, at the time when a main processor 1 acquires the command area 5, the head pointer area 4 and the pointer copy area 7 are compared. Thus, the processing such as the release and the acquisition of the storage area, etc., is surely performed, and in addition, the burden of the processor to perform such control is reduced.
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