To ensure economical operation by constantly monitoring operating conditions without spending extra time or manpower.

An operation monitor circuit 12 automatically forces an engine into a shutdown state as soon as a parking brake is operated into a parking position or after a predetermined period of time has elapsed while a vehicle remains stationary. This helps prevent fuel from being wasted while the vehicle remains stationary. In addition, this device determines the current operating mode and causes an alarm buzzer to sound when an engine speed or vehicle speed reaches a predetermined value corresponding to a normal-speed mode while the vehicle is running on an ordinary road (normal mode), and when the engine speed or vehicle speed reaches a predetermined value corresponding to a high-speed mode while the vehicle is running on an expressway (high-speed mode). This allows engine speed and vehicle speed optimum for each current operating mode to be retained, which ensures both economical and safe driving.