A method for controlling posture of a marine vessel with posture control tabs (21A, 21B) mounted on a stern of a hull of the marine vessel to control a posture of the hull, and actuators (22A, 22B) to actuate the posture control tabs (21A, 21B), the method comprises judging whether or not the hull is being loaded onto a trailer on a basis of a speed of the hull and a pitch angle of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a number of engine revolutions of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a speed of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a throttle opening angle of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a speed of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of an acceleration of the hull and a pitch angle of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a number of engine revolutions of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and an acceleration of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a throttle opening angle of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and an acceleration of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a throttle opening angle of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a pitch angle of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a number of engine revolutions of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a pitch angle of the hull; and, upon judging that the hull is being loaded onto the trailer, controlling the actuators (22A, 22B) to position the posture control tabs (21A, 21B) at retracted positions. judging whether or not the hull is being loaded onto a trailer on a basis of a speed of the hull and a pitch angle of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a number of engine revolutions of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a speed of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a throttle opening angle of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a speed of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of an acceleration of the hull and a pitch angle of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a number of engine revolutions of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and an acceleration of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a throttle opening angle of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and an acceleration of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a throttle opening angle of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a pitch angle of the hull, or judging whether or not the hull is being loaded onto a trailer on a basis of a number of engine revolutions of a propulsion device including an engine (16A, 16B) to generate a propulsive force to move the hull and a pitch angle of the hull; and, upon judging that the hull is being loaded onto the trailer, controlling the actuators (22A, 22B) to position the posture control tabs (21A, 21B) at retracted positions.