A power transmission apparatus includes a driving joint unit having a first driving gear fixed to a first driving shaft and a second driving gear fixed to a second driving shaft, an operating joint unit fixed on an operating shaft and having an operating gear rotating together with the operating shaft, a first operating belt connected to the first driving gear and the operating gear, a second operating belt connected to the second driving gear and the operating gear to apply a torque in opposite directions, a driving link having one end connected to the first driving shaft or the second driving shaft and the other end connected to the operating shaft, and an operating link fixed to the operating shaft.