There exist various studies on underactuated control methods so far, but most of them are confined into the case of systems with two inputs, and therefore there are a few studies for systems with three or more inputs. In this paper, a fire truck robot that is an underactuated system with three inputs is considered as a controlled object, and a switching control method based on an invariant manifold theory is proposed for stabilizing it, where a chained form model is assumed to be used as a canonical model. It is expected that each state of the controlled object will be converged smoothly to the origin by using this type of control. The effectiveness of the proposed method is demonstrated through simulations. © 2012 The Authors.