PURPOSE: To detect a defective address of a magnetic bubble memory easily without using a specific measuring device and a testing device by detecting the defective address on the basis of a normal address.

CONSTITUTION: A storage device 1 is driven and address data are successively sent to an address data reading line 11. If address data stored in a magnetic bubble memory (BM) 10 are defective, the compared result of the address data by a comparator 12 are inconsistent, so that a CPU 2 decides that the address data are defective and changes the specified address data to an address specification line 13. When address matching information is obtained, the CPU 2 sends the address (A+1) to the address specification line 13 on the basis of the current address A to decide whether the corresponding address of the BM 10 is correct or not. If a defective address is detected, the CPU 2 reads out the defective address data from the BM 10 through an address data transfer line 15 and compares the read out data with the specified address data sent to the address specification line 13 to detect a defective bit.