PURPOSE: To attain safety by stopping an engine even when tumbled and striking the front side while in a device whereby safety of backward running can be improved by stopping the engine when a cultivator, mainly during its backward running (reverse running), is tilted to the front by reaction force.

CONSTITUTION: A movable unit 2 is made swivelable against a fixed unit 1 in a front side of a cultivator. A fixed side rise up part 6 and a movable side rise up part 7 are protrusively provided respectively in the fixed unit 1 and the movable unit 2. At least one of the fixed/movable side rise up parts 6, 7 is formed of flexible material, further to provide in an upper end side respectively of the fixed/movable side rise up parts 6, 7 a fixed/movable side terminal part 8, 9 opposed contactable/separable. Any one of the fixed/movable side terminal parts 8, 9 is grounded to a cultivator main unit, to insulate the other therefrom, further to connect the other to a stop circuit wiring 24 from a generating set 22. A device is formed by normally separating the fixed side terminal part 8 from the movable side terminal part 9.