In an apparatus for controlling operation of an outboard motor having an internal combustion engine and transmission, it is configured to control operation of the transmission to change the gear position to the first or second speed in response to a speed change command outputted upon an operator's manipulation, determine whether a throttle valve of the engine is at a fully-opened position or thereabout when the speed change command to the first speed is outputted, and determine whether the engine is under a predetermined operating condition when the throttle valve is determined to be at the fully-opened position or thereabout, wherein the transmission controller changes the gear position from the first speed to the second speed when the engine is determined to be under the predetermined operating condition. With this, it becomes possible to mitigate load on a transmission gear to improve durability of the transmission.