An exercise device comprises a frame, a rotational mechanism, a left and a right coupling mechanism, and an adjusting assembly. A post structure is upwardly extended from the front portion of the frame. The rotational mechanism is arranged at the post structure. The left and right coupling mechanisms are arranged at a side of the post, respectively. One end of the left and right coupling mechanism couples to the rotational mechanism, and the other end respectively comprise a left and a right pedal assembly making a moving path. The adjusting assembly comprises a left and a right linkage structures with two ends, in which one end couples to the post and the other end moveably couples to the left and right pedal assembly. By changing the angles between the left and right linkage structures and the post structure, the pedal assemblies are moved to determine a step distance.