PURPOSE: To prevent to unjustly start the engine of an automobile due to the use of a reproduced key or direct connection of wire.

CONSTITUTION: A secret certification symbol is recorded on a magnet card 1 in which a plurality of permanent magnets 4 are embedded in a certain developing pattern, by combination of existence of the permanent magnet 4 on the magnetic record part position or the magnetic direction of the permanent magnet 4. Meanwhile, the secret certification symbol recorded on the magnet card 1 is read out with the magnetism detector 8 in a card reader 6 formed with a slit 7 for inserting the magnet card 1, mounted in the automobile, and compared with a previously set reference secret certification symbol with a comparator 12. When both coincide with each other, a coincidence signal is taken out from the comparator 12, and the electric circuit necessary for running of the automobile is controlled by the coincidence signal.