PURPOSE: To improve the reliability of a security apparatus started and stopped by a portable transmitting unit by starting the security operation in response to an arming signal from the transmitting unit when an automatic transmission is on a P position.

CONSTITUTION: An arming reception monitoring section 24 for receiving the output signals of a transmission position detecting sensor 32 and door opening- closing sensor 31 is provided to send an H signal from the monitoring section 24 and provide a condition capable of arming when a speed change position is on a P position and the opening and closing of a door is detected, while timing is started. Whether or not a predetermined time elapses since the timing start is checked to provide a condition incapable of arming after the passage of the predetermined time. When a security control section 25 receives an arming command from a remote control unit 1 under the condition capable of arming, whether or not abnormalities are detected is monitored. A siren is blown in the occurrence of the abnormalities while a process to prohibit engine start is carried out.