PURPOSE: To execute a ring buffer operation by using only a bank whose memory function is normal, in plural banks obtained by dividing a storage area of a buffer memory.

CONSTITUTION: By a CPU 1, a memory check of each bank of a buffer memory 2 is executed, and the head address (pointer) of the bank whose memory function is normal is set to an address holding means 9. A write address generating means 11 and a read address generating means 12 read out cyclically the pointer of the held bank, designate the bank of the buffer memory 2, and generate an address in the bank.