PURPOSE: To attain a ciphering device which erases automatically stored confidential information against an external incorrect access by providing a means outputting an incorrect access signal when a shift signal is detected for the output regardless of no access start signal output.

CONSTITUTION: An access start detection circuit 21 generates an access start signal when a lock is released for the purpose of starting internal access, a rod 13 is detached upward in the figure, a plate spring 15' is released and contacts are opened. A shift detection circuit 22 generates a shift signal, when the 2nd switch circuit 12 and a projection 14 are shifted, that is, a main body section is shifted to some degree in the enclosure or the main body section is removed to the outside, the plate spring 15 is opened and the contacts are interrupted. Further, a decision circuit 23 generates an incorrect access signal by deciding it as the presence of an incorrect access that the output of the shift signal is detected regardless that no access start signal is generated. An erase signal generating circuit 24 erases the confidential information stored in a memory 25 by generating a signal when the incorrect access signal is received.