PURPOSE: To secure the safety of a driver by an alarm or a measure for stopping an engine when a vehicle took a posture having possibility of falling, by processing signals from a before-and-behind variable (X) sensor and a left- and-right variable (Y) sensor by CPU.

CONSTITUTION: An X-sensor 5 and a Y-sensor 7 are mounted on the center of agricultural machine main body so as to be angularily displaced by 90° in a horizontal direction and constituted of movable contacts 51a, 71a and variable resistors 51b, 71b respectively fixed to freely swingable arms. The X-sensor 5 and the Y-sensor 7 are connected to a first interface (A/D converter)8 and the outputs of the sensors 5, 7 are converted to digital signals which are, in turn, respectively inputted to the input board of CPU9. CPU operates a bank angle from said inputs and, when the bank angle is a limit or more, an alarm means 11 is operated through a second interface 10 not only to emit an alarm but also to stop an engine.