A ladder truck with lift mechanism has played an important role in life-saving and fire-fighting. Although the quicker operation mechanism is requested for these demands, the lift operation generates a lot of vibration at the time of the extending and retracting motions, the ascending and descending motions, and turning motion. In this paper, though an actual ladder truck is composed of five sections, a two-sections ladder model is investigated to make the physical understanding easier. A coupled equation of the model is derived using the differential algebraic equation.