A riding device includes an intermediate base pivotally assembled on a bottom base and having the opposite ends respectively provided with a front and a rear vertical spindle. The front spindle has each end fixed with a crank, and the rear spindle has each end movably connected with a swing arm. The cranks and the swing arms have their upper ends respectively connected with four feet of a seat plate. A transmission unit fixed on the intermediate base includes a motor for driving a first, a second and a third gear to rotate. The third gear is secured on the front spindle. A pull rod has its upper end connected with the second gear by a universal bearing and its lower end connected with the bottom base. When the motor started, the seat plate can be actuated by interaction to swing back and forth, up and down and left and right.