In an apparatus for controlling operation of an outboard motor mounted on a boat and having a torque converter equipped with a lockup clutch, it is configured to calculate a speed ratio of the torque converter based on an input rotation speed and output rotation speed of the torque converter, detect manifold absolute pressure of the engine, control the lockup clutch to ON when the calculated speed ratio has been equal to or greater than a reference value, and control the lockup clutch to OFF when the manifold absolute pressure has been decreased by a first predetermined value or more. With this, it becomes possible to prevent the boat speed from decreasing even when the resistance of water flow acting on the boat increases due to the influence of a wave etc., thereby maintaining the maximum speed.