In an apparatus for controlling operation of an outboard motor that has an internal combustion engine equipped with a plurality of cylinders and is configured to switch a shift position between an in-gear position that enables engine's driving force to be transmitted to a propeller and a neutral position that cuts off transmission of the driving force, it is configured such that a neutral operation detector detects a neutral operation in which the shift position is switched from the in-gear position to the neutral position; a driving force controller conducts driving force decreasing control to decrease the driving force when the neutral operation is detected; and a cylinder number changer detects an engine speed variation range during the driving force decreasing control and, of the plurality of the cylinders, determines and changes the number of the cylinders with which the control is to be conducted based on the variation range.