In an apparatus for controlling operation of an outboard motor having an internal combustion engine, a transmission, and a trim angle regulation mechanism, where operation of the transmission is controlled to change the gear position from a second speed to a first speed when detected throttle change amount not less than a first predetermined value and operation of the trim angle regulation mechanism is controlled to start the trim-up operation such that the trim angle converges to a predetermined angle, the operation of the trim angle regulation mechanism is controlled such that the trim angle is decreased based on the detected rudder angle when steering of the outboard motor is started, thereby enabling to appropriately prevent cavitation caused by steering of the outboard motor, so that the boat can be smoothly turned.