A pedal exercise machine includes an arc trajectory with a length adjustment for adjusting the lengths of pedal trajectories and arm levers, an angle adjustment for adjusting the position of the pedal trajectory, and a displacement mechanism for adjusting the pedals' angles relative to the ground. The pedal exercise machine includes a base, a front frame and a center frame, coupled together, a pair of pedals, a pair of pedal links, and a pair of subsidiary pedal links, which are coupled to the respective pedals by shafts different from shafts which the respective pedal links are coupled to the corresponding pedals. The pedal exercise machine further includes a resistance pulley, a crank shaft, and a pair of crank link units. Each crank link unit has the angle adjustment mechanism configured to adjust the angle between the corresponding pedal link and the corresponding crank link unit.