An engagement device includes: an engaged body configured to rotate in conjunction with a rotary shaft; an engaging body arranged coaxially with the engaged body and configured to engage with the engaged body by movement in an axial direction; a power source configured to provide thrust to the engaging body in the axial direction; and a hub member configured to couple the engaging body to a torque receiver which receives torque transmitted from the engaged body at a time the engaging body engages with the engaged body. The engaged body, the engaging body, and the power source are accommodated in a closed space, and the hub member is at least a part of an outer shell forming the closed space.