Abstract: A safety system for a lawn mower having an engine, a propelling transmission line for transmitting drive from the engine to drive wheels, and a PTO transmission line for transmitting drive from the engine to a grass cutting unit. An engine start is allowed when the propelling transmission line is inoperative. The engine is stopped when the propelling transmission line is operative and a driver is in a non-driving state. A steering section includes an arch-like steering handle, and an auxiliary handle having a shape substantially corresponding to the steering handle and pivotable from an upper position projecting above the steering handle and a lower position depressed below the steering handle. The driver is determined to be in the driving state when the auxiliary handle is in an intermediate position adjacent the steering handle.