An embodiment power transmission device includes an input shaft rotatable about a first rotation axis, first and second wires wound around an outer surface of the input shaft based on a first radial direction, each having a first side fixed to the input shaft, an output shaft rotatable about a second rotation axis, the output shaft including a shaft body, wherein the first and second wires surround an outer surface of the shaft body based on a second radial direction, and first and second wire holders to which a second side of the first wire and a second side of the second wire are respectively fixed. The first wire extends in a first circumferential direction of the shaft body, and then the first wire extends in a second circumferential direction opposite to the first circumferential direction of the shaft body.