An overturn prevention control device includes a bicycle robot capable of freely laterally inclining, an angular velocity sensor mounted on the bicycle robot such that a detection axis thereof extends in a substantially longitudinal direction of the bicycle robot, a motor mounted on the body such that a rotating shaft thereof extends in a substantially longitudinal direction of the body, a rotation sensor that detects a rotational position or a rotational speed of the motor, and an inertial rotor coupled to the rotating shaft of the motor. The overturn prevention control device corrects inclination of the bicycle robot by rotating the inertial rotor using the motor and by utilizing a reaction torque occurring when the inertial rotor is rotated. The overturn prevention control device further includes an inclination angle estimating portion arranged to estimate an inclination angle relative to a balanced state.