Oscillation of ropeway carrier is caused by wind, track rope vibration, and vibration when the carrier passes through column. In a certain ropeway installation, a carrier without lateral sway damping device significantly rolled after passing through column, and consequently collided with the wayside wall. In this paper, measurement of rope sag and motion of the carrier is conducted to investigate the phenomenon. The measurement result shows that roll angle of the carrier under loaded condition tends to grow when the carrier runs toward column even if effect from crosswind is small. It is estimated that transition of the rope sag affects the roll motion of the carrier. This paper also shows dynamics simulation to grasp the influence of freedom of track rope on the rolling motion of the carrier. In the simulation, the carrier is modeled as a single pendulum. Time variation of rope sag is expressed as a change of length of pendulum or lateral vibration of fulcrum of pendulum. Transition of roll vibration period and growth of roll angle are discussed.