To provide a security system for a civil-engineering and construction machine capable of facilitating the recovery of any stolen machine upon finding the fact of theft as early as in its transit.

The civil-engineering and construction machine to which the invention applies is equipped with a position sensing means using a GPS etc., a vibration sensor to sense swinging of the machine, and a signal transmitter to transmit the information via a communication circuit, wherein the ID number of the machine and its position information are transmitted via the communication circuit in case the sensor has sensed vibration while the machine is in the condition out of function with its engine key removed.