PURPOSE: To restart any operation once stopped easily and surely with a simple constitution, by using a memory chip storing anddetecting the internal state of the memory chip.

CONSTITUTION: Position information and memory address information loops 10,11 provided with bubble detectors 13,14 and the like, the same as major and minor loops 3,2 of the memory chip 8 are formed on a state display chip 9. This loop 10 is provided with a position 12 on which a bubble is transferred via a transfer gate controlled synchronizingly with the chip 8, and the transfer of bobble with the loop 10 is synchronized with the transfer between the loops 2 and 3. Thus, when the detector 13 detects the bubble transferred on the loop 10 in response to the rotating magnetic field at the restart after the power supply interruption, the position information of the loop 3 is obtained and the loop 3 is initialized. When no output exists in the detector through this circulation, it is confirmed that no buble is transferred to the loop 2. This is the same for the address information via the loop 11, and the restart after operation stop is done easily and surely.