A climbing machine having a single circulating transmission path structure is disclosed. The climbing machine includes a frame body, a first slide rail assembly, a second slide rail assembly, and a transmission unit. A transmission assembly of the transmission unit is continuously connected with a first pedal slider, a second pedal slider, a first handle slider, a second handle slider to form a single circulating transmission path instead of two independent paths on both sides of the frame body. The smoothness of the transmission path can be improved without the need for timing belts or connecting belts.