A transmission device applied to rotary shafts for facilitating the assembling process. The transmission device includes at least one rotary shaft, a drive member movable along with the rotation of the rotary shaft, a transversely movable driver, a turning unit and a transmission unit. The turning unit has a first end connected with the driver and a second end assembled with the transmission unit. When the transmission unit is longitudinally moved, a connection section and a carrier body are driven by the transmission unit to lift or lower a base body or a frame in accordance with the operation mode of an electronic apparatus.