Abstract: A security system for controlling the operation of releasing a lock mechanism for locking a steering mechanism of a mobile medium such as a vehicle. This system is provided with at least one information medium such as a license card on which information which identifies the operator of the mobile medium stored, a reading device for reading out the information stored in the information medium, a memory device in which information which is the same as the information stored on the information medium is stored previously and a comparing device which compares an output from the reading device with the contents of the memory device and which outputs a lock-release signal for releasing the lock mechanism when a match occurs in this comparison. The security system further may include writing means by which the contents of the memory device may be rewritten if the output of the reading device coincides with the contents of the memory device.