SEAT DEVICE

A seat device that can reliably prevent a rotation operation of a seat by a seated person, in a long state where the back of the seat is along a wall. A rotation lock mechanism () that can restrain the rotation of a seat (), a rotation operation unit () that performs a release operation of restraint by the rotation lock mechanism (), and a rotation operation prevention mechanism () that disables the release operation in the rotation operation unit (), when the seat () is in the long state are included. The rotation operation prevention mechanism () includes an engaging unit () provided in the leg stand (), and an engaged unit () that is provided in the rotation operation unit () in the movable stand (), and disables the release operation in the rotation operation unit () by being engaged with the engaging unit () when the seat () is in the long state.