A transmission device, comprising: an input component, comprising an inner gear ring, a first gear and a second gear both coaxial with the inner gear ring, and a third gear in functional connection to the first gear, both of the first gear and the second gear being mounted on an input shaft, the first gear driving the third gear to rotate, the third gear having a first end engaged with the inner gear ring and being capable of rotating or revolving, and the third gear having a second end arranged outside the inner gear ring; a unidirectional control mechanism fixed at a preset position, the unidirectional control mechanism comprising a first unidirectional component arranged near the inner gear ring, the first unidirectional component comprising a first rotating member that can unidirectionally rotate in a first rotation direction, the first rotating member being fixedly connected to the inner gear ring; and an output component, comprising at least two fourth gears arranged at an interval in a circumferential direction, the third gear being revolvable to a position in which the second end of the third gear is arranged on an inner side of one of the at least two fourth gears and, the third gear being selectively engageable with any one of the fourth gears; characterized in that, the transmission device further comprises a rotary component, comprising a fifth gear that rotates in a direction opposite to rotation direction of the third gear and a rotary box (412, 414) for housing the first gear, the second gear and the third gear, the fifth gear being arranged on the rotary box (412, 414) in a rotatable manner, the fifth gear having a first end 422) in functional connection to the second gear and being driven by the second gear to rotate, the fifth gear being selectively engageable with any one of the fourth gears and the fifth gear having a second end whereby the fifth gear is revolvable to a position in which its second end is arranged on an outer side of one of the at least two fourth gears, and the third gear being mounted in the rotary box (412, 414) and capable of driving the rotary box (412, 414) to rotate; and the first gear having a diameter different from that of the second gear. an input component, comprising an inner gear ring, a first gear and a second gear both coaxial with the inner gear ring, and a third gear in functional connection to the first gear, both of the first gear and the second gear being mounted on an input shaft, the first gear driving the third gear to rotate, the third gear having a first end engaged with the inner gear ring and being capable of rotating or revolving, and the third gear having a second end arranged outside the inner gear ring; a unidirectional control mechanism fixed at a preset position, the unidirectional control mechanism comprising a first unidirectional component arranged near the inner gear ring, the first unidirectional component comprising a first rotating member that can unidirectionally rotate in a first rotation direction, the first rotating member being fixedly connected to the inner gear ring; and an output component, comprising at least two fourth gears arranged at an interval in a circumferential direction, the third gear being revolvable to a position in which the second end of the third gear is arranged on an inner side of one of the at least two fourth gears and, the third gear being selectively engageable with any one of the fourth gears; characterized in that, the transmission device further comprises a rotary component, comprising a fifth gear that rotates in a direction opposite to rotation direction of the third gear and a rotary box (412, 414) for housing the first gear, the second gear and the third gear, the fifth gear being arranged on the rotary box (412, 414) in a rotatable manner, the fifth gear having a first end 422) in functional connection to the second gear and being driven by the second gear to rotate, the fifth gear being selectively engageable with any one of the fourth gears and the fifth gear having a second end whereby the fifth gear is revolvable to a position in which its second end is arranged on an outer side of one of the at least two fourth gears, and the third gear being mounted in the rotary box (412, 414) and capable of driving the rotary box (412, 414) to rotate; and the first gear having a diameter different from that of the second gear.