A trochoid propulsion system includes wheels provided at three points of the outer edge of an outer wheel part that turns around a driving shaft; and a steering link part that co-rotates with the action part and is movable horizontally on a turning plane. The steering link part includes a liner slider including a guide member attached to a vertical steering shaft that rotates each wheel so that the length direction is in a radial direction of the steering shaft and a moving member that slides on the guide member. In a state where a center of rotation of the steering link part coincides with the driving shaft of the outer wheel part, a rotating shaft provided corresponding to the steering shaft is attached rotatably to the corresponding moving member at a position separated from the steering shaft by a predetermined distance.