In an apparatus for controlling operation of an outboard motor having an engine to power a propeller, a transmission being selectively changeable in gear position to establish speeds including a first speed and second speed and transmitting power of the engine to the propeller with a gear ratio determined by established speed, and a trim angle regulation mechanism regulating a trim angle through trim-up/down operation, the transmission is controlled to change the gear position from the second speed to the first speed when the second speed is selected and a throttle opening change amount is at or above a predetermined value; and the trim angle regulation mechanism is operated to start the trim-up operation based on engine speed. With this, the transmission can be appropriately controlled to suppress the decrease in boat speed caused by change of gear position, thereby mitigating an unnatural feel given to the operator.