This paper aims at the problem of two dimensional load sway caused by horizontal motion of booms in rotary crane systems, and proposes a control method using only horizontal boom motion for achieving boom positioning control and load sway suppression control simultaneously. Firstly, we derive a partial linearized dynamic model of a rotary crane by using a disturbance observer. The model has robustness with respect to varying parameters such as joint friction and load mass. Next, we design a nonlinear controller on the basis of the model, and confirm the stability of the control system via Lyapunov stability theory. Finally, comparative simulations and experimental results demonstrate the effectiveness of the proposed method. A kind of rotary crane without an actuator for vertical boom motion can be achieved by using the proposed method, therefore, the structure of cranes can be simplified and their production cost can be reduced.