Security device for vehicle

A security device for vehicle disclosed is of a type generating a seed that is used suitably in order to generate a key by being encoded and that is decreased in regularity. Namely, the security device for vehicle according to the present invention has a construction that generates from vehicle control data the seed used for generating an authentication key on the vehicle side and a key on the user side by being encoded. By such construction, the seed is generated from the vehicle control data concerning the constituent elements of the vehicle that are kept in a state of operation. Since the vehicle control data itself is a type that momentarily changes in correspondence with the state of operation of the constituent elements of the vehicle, thus generated seed exhibits substantially no regularity to thereby become a very good kind of random number.