An engine control apparatus includes: a stop switch body 6; a stop switch knob 3; a lock plate 5; a transponder 9 that is provided at the lock plate side and that can transmit a predetermined ID code; and a control section 11 that can receive the ID code transmitted from the transponder 9 and that controls based on the ID code the engine operation of the small motorboat. The engine control apparatus is structured such that, when the lock plate 5 is disengaged from the stop switch knob 3, the stop switch body 6 is activated to allow the engine to stop or to be in an idling state. The engine control apparatus also includes the writing section 16 for writing a regular ID code of a transponder to another transponder.