An underwater sailing body includes: a positioning device configured to detect positional information of a hull of the underwater sailing body; a posture detecting sensor configured to detect posture information of the hull; an actuator configured to apply thrust to the hull in a front-rear direction of the hull, a left-right direction of the hull, an upper-lower direction of the hull in water to change the position and posture of the hull; and a controller configured to control the actuator. In order to hold a hull at a target position when the hull receives an external force by disturbances, the hull keeps balance by using thrusters with respect to the external force acting on the hull. Specifically, the hull is held at the target position by controlling a thruster configured to generate thrust in a front-rear direction and a thruster configured to generate thrust in a left-right direction.