Torque of a prime mover is input into a sun gear. A planetary gear revolves in a circumferential direction of the sun gear while rotating and meshing with the sun gear. A carrier has an annular shape, rotatably supports the planetary gear, and is rotatable relative to the sun gear. A first ring gear is fixed to a housing, and meshes with the planetary gear. A second ring gear meshes with the planetary gear, is different from the first ring gear in number of teeth of a tooth portion, and outputs torque to a rotation portion. At least a part of the sun gear in an axial direction is located radially inward of the carrier. At least a part of the first ring gear and at least a part of the second ring gear in the axial direction are located radially outward of the carrier.

A state changing unit is capable of contacting a clutch, and being configured to receive a force along the axial direction from a translation portion and change a state of the clutch to an engaged state or a disengaged state according to a position of the translation portion in an axial direction relative to a housing. A fixed end is non-rotatable relative to the housing. A return spring is disposed on a side of the fixed end opposite to the clutch, and capable of urging the translation portion in a direction away from the clutch with respect to the fixed end.

A state changing unit is capable of contacting a clutch, and being configured to receive a force along the axial direction from a translation portion and change a state of the clutch to an engaged state or a disengaged state according to a position of the translation portion in an axial direction relative to a housing. A fixed end is non-rotatable relative to the housing. A return spring is disposed on a side of the fixed end opposite to the clutch, and capable of urging the translation portion in a direction away from the clutch with respect to the fixed end.

A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

A prime mover is provided in a housing, and can operate by energization and output a torque. A speed reducer can decelerate and output the torque of the prime mover. A rotational translation unit including a rotation portion that rotates relative to the housing when the torque output from the speed reducer is input, and a translation portion that moves relative to the housing in an axial direction when the rotation portion rotates relative to the housing and can change a state of a clutch to an engaged state or a non-engaged state. The speed reducer includes an output unit that outputs the decelerated torque of the prime mover to the rotation portion. The rotation portion is formed of a material different from that of the output unit separately, and is provided to be rotatable integrally with the output unit.

A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

A housing includes an accommodation space for a prime mover and a speed reducer. A rotational translation unit includes a rotation portion that rotates relative to the housing upon receiving torque outputted from the speed reducer, and a translation portion that moves relative to the housing in an axial direction according to rotation of the rotation portion. The accommodation space is between the rotation portion and the housing. A clutch in a clutch space allows or interrupts transmission of torque between a first transmission portion and a second transmission portion. The rotation portion is between the clutch space and the accommodation space. A sealing member has an annular shape in contact with the rotation portion, and maintains an air-tight or liquid-tight state between the accommodation space and the clutch space.

Torque of a prime mover is input into a sun gear. A planetary gear revolves in a circumferential direction of the sun gear while rotating and meshing with the sun gear. A carrier has an annular shape, rotatably supports the planetary gear, and is rotatable relative to the sun gear. A first ring gear is fixed to a housing, and meshes with the planetary gear. A second ring gear meshes with the planetary gear, is different from the first ring gear in number of teeth of a tooth portion, and outputs torque to a rotation portion. At least a part of the sun gear in an axial direction is located radially inward of the carrier. At least a part of the first ring gear and at least a part of the second ring gear in the axial direction are located radially outward of the carrier.

Torque of a prime mover is input into a sun gear. A planetary gear revolves in a circumferential direction of the sun gear while rotating and meshing with the sun gear. A carrier has an annular shape, rotatably supports the planetary gear, and is rotatable relative to the sun gear. A first ring gear is fixed to a housing, and meshes with the planetary gear. A second ring gear meshes with the planetary gear, is different from the first ring gear in number of teeth of a tooth portion, and outputs torque to a rotation portion. At least a part of the sun gear in an axial direction is located radially inward of the carrier. At least a part of the first ring gear and at least a part of the second ring gear in the axial direction are located radially outward of the carrier.