An exercise bike includes a frame, a driving member, two sun gears, two swing arms, two planet gears, and two cranks. The driving member is assembled to the frame and has a shaft extending from two sides of the frame. The two sun gears, the two swing arms, the two planet gears, and the two cranks are respectively assembled to the two sides of the frame. For each set, the crank drives the planet gear to rotate so as to drive the swing arm to rotate the shaft, and the planet gear is rotated around the sun gear. Accordingly, a pedal connected to each of the cranks moves around the axis of the corresponding planet gear.