In the event that an electronic apparatus having a security function is forcibly put into an inoperable state because electric power is shut off once by an operation equivalent to theft, the inoperable state can be canceled by using a code notified by the dealer by telephone, without carrying the electronic apparatus in its dealer. After electric power is supplied again, the vehicle-mounted compact disc (abbreviated as CD) reproduction apparatus is used to play back a CD, and its TOC information is used as a judgment identification code C1. When the code C1 is identical to the authorized identification code A21, the electronic apparatus is made operable. In order to cancel the inoperable state after the number of inconsistencies becomes 10 or more, the individual code A22 of an EEPROM 21 is indicated and notified to the dealer. The dealer carries out calculation by using the individual code A22, and a result B2 of the calculation is notified to the user. The user inputs the calculation result B2. Individual code calculating means carries out the same calculation as the above-mentioned calculation and obtains the calculation result B3. When the calculation result B2 coincides with the calculation result B3, the inoperable state can be canceled.