In an apparatus for controlling posture of a small boat having a hull and an even number of outboard motors mounted side by side on a stern of the hull, each equipped with a propeller driven by an engine and a throttle actuator adjusting a throttle valve opening of the engine, an inclinometer is installed in one of the outboard motors that produces an output indicating inclination of the hull relative to a vertical axis around a roll axis. It is determined whether the hull inclines to port or starboard from the output of the inclinometer and when it does, operation of the throttle actuators of the outboard motors are controlled on a side determined to incline downward to increase engine speed, while controlling operation of the throttle actuator of the outboard motor on a side determined to incline upward to decrease the engine speed.