PURPOSE: To hold the secret of contents in a memory by outputting data read out of the memory while arbitrarily exchanging the bits of the data so that the third personnot knowing which bit is exchanged can not know the correct data.

CONSTITUTION: Under the control of a CPU 1, the content output start address of a ROM 3 is set to a program counter 4, and this address is outputted from the counter 4 to the ROM 3. A ROM data corresponding to this address is outputted from the ROM 3 to a data bus 6 and inputted to a bit switching circuit 7. At the circuit 7, the bits are exchanged, and the result is outputted to an input/output port 5. Afterwards, the counter 4 increases or decreases the contents, the data in the ROM 3 are successively outputted to the circuit 7 and at the circuit 7, the inputted data in the ROM 3 are successively outputted to the input/output port 5 while exchanging the bits.