A control device (60) of a mobile body (1) calculates a center-of-gravity displacement degree index value representing an estimate of the degree of displacement of the center of gravity of the operator in the lateral direction from a prescribed reference position with respect to a vehicle body (2), and determines a control input for an actuator (15) which can cause a moment in the roll direction to act on the vehicle body (2) so as to reduce the degree of displacement of the center of gravity of the operator indicated by the center-of-gravity displacement degree index value. The control device (60) controls the actuator (15) in accordance with the control input.