PURPOSE: To make illegal read-out impossible by executing read-out by an array sequence formed by combining an identification number inputted at the time of read-out, and a random number stored at the time of write.

CONSTITUTION: When an identification number is inputted from an identification number input device 18, a pseudo random number is generated by a random number generating circuit 19, and this random number is stored in a random number storage circuit 20. Also, simultaneously, a data storage sequence corresponding to the inputted identification number and the generated random number is generated, and bit data from data lines 9-12 are stored in the corresponding memory cells, respectively. In such a state, when the identification number is inputted from the input device 18, the random number stored at the time of write is inputted to a selector control circuit 17 from the random number storage circuit 20, a selective instruction of the data line corresponding to the identification number and the random number is generated, and transferred to each selector 5-8. As a result, each selector 5-8 outputs the data stored in each memory cell 21-24 to the corresponding data lines 9-12 in accordance with its instruction.