A washing machine comprising: a body; a drum rotatably installed inside the body; a pulley configured to transmit a torque to the drum; and a shaft configured to connect the drum to the pulley, wherein the pulley comprises a shaft insertion hole with a first opening into which the shaft is inserted, wherein the shaft insertion hole comprises a first toothed portion provided in the inner circumferential surface of the shaft insertion hole, and the shaft comprises a second toothed portion disposed on an outer circumferential surface of one side of the shaft, which is to be inserted into the shaft insertion hole, and configured to be engaged with the first toothed portion, wherein the first toothed portion comprises an inner circumferential surface extended obliquely with respect to the rotation axis of the pulley, so that when the shaft is coupled to the shaft insertion hole by being inserted into the shaft insertion hole, at least one part of the first toothed portion is not in contact with the second toothed portion, wherein the first toothed portion comprises a guide surface disposed at an end of the first toothed portion adjacent to the first opening into which the shaft is inserted, and formed in a diagonal shape to guide the insertion of the shaft, and characterized in that the shaft insertion hole comprises a taper portion provided at a rim of the first opening disposed on one side into which the shaft is inserted, and extended obliquely and outwardly with respect to the rotation axis of the pulley, and the inner circumferential surface of the first toothed portion comprises a first section in which the radius of the second toothed portion of the shaft is greater than the radius of the shaft insertion hole and the inner circumferential surface of the pulley is in contact with the outer circumferential surface of the shaft and a second section disposed between the guide portion and the first section and adjacent to the guide portion, wherein the second section extends obliquely with respect to the rotation axis of the pulley and with respect to the outer circumferential surface of the second toothed portion of the shaft, so that the first toothed portion is not in contact with the second toothed portion in the second section. a body; a drum rotatably installed inside the body; a pulley configured to transmit a torque to the drum; and a shaft configured to connect the drum to the pulley, wherein the pulley comprises a shaft insertion hole with a first opening into which the shaft is inserted, wherein the shaft insertion hole comprises a first toothed portion provided in the inner circumferential surface of the shaft insertion hole, and the shaft comprises a second toothed portion disposed on an outer circumferential surface of one side of the shaft, which is to be inserted into the shaft insertion hole, and configured to be engaged with the first toothed portion, wherein the first toothed portion comprises an inner circumferential surface extended obliquely with respect to the rotation axis of the pulley, so that when the shaft is coupled to the shaft insertion hole by being inserted into the shaft insertion hole, at least one part of the first toothed portion is not in contact with the second toothed portion, wherein the first toothed portion comprises a guide surface disposed at an end of the first toothed portion adjacent to the first opening into which the shaft is inserted, and formed in a diagonal shape to guide the insertion of the shaft, and characterized in that the shaft insertion hole comprises a taper portion provided at a rim of the first opening disposed on one side into which the shaft is inserted, and extended obliquely and outwardly with respect to the rotation axis of the pulley, and the inner circumferential surface of the first toothed portion comprises a first section in which the radius of the second toothed portion of the shaft is greater than the radius of the shaft insertion hole and the inner circumferential surface of the pulley is in contact with the outer circumferential surface of the shaft and a second section disposed between the guide portion and the first section and adjacent to the guide portion, wherein the second section extends obliquely with respect to the rotation axis of the pulley and with respect to the outer circumferential surface of the second toothed portion of the shaft, so that the first toothed portion is not in contact with the second toothed portion in the second section.