An emergency engine shutoff apparatus for shutting off an engine in an accident of a ship having a hull and an outboard engine system is provided which includes: an acceleration detector for detecting an acceleration applied in a longitudinal direction of the hull and an acceleration applied in a vertical direction of the hull; an accident determining apparatus for determining that a collision accident occurred when the acceleration applied in a longitudinal direction of the hull exceeds a threshold, and for determining that a capsize accident occurred when a roll angle of the ship exceeds a threshold, the roll angle being arithmetically operated by using the acceleration in the vertical direction; and an engine shutoff apparatus for shutting off the engine by stopping fuel supply to the engine when it is determined that a collision accident or a capsize accident occurred.