The invention discloses a three-position transmission device which comprises a shell, a base, grounding switches, isolating switches and an inner crank arm. The grounding switches and the isolating switches are vertical to each other and are arranged in the base; the inner crank arm is rotationally installed in the shell; one grounding switch and one isolating switch are selected for transmission so as to be switched on, or the grounding switches and the isolating switches are switched off. Compared with the prior art, the three-position transmission device has a simpler structure, consequently can save cost, and is easy to assemble and easy to use.