To provide a seat for a vehicle, an aircraft, or the like which is equipped with a seat part and a backrest part and has a seat support on a side surface of a long side of a seat part and a backrest support on a side surface of a long side of a backrest part on the both sides of the central, longitudinal surface of the seat, and to hold a passenger using the seat from the sides with a seat support and a backrest support.

The seat support and the backrest support are made adjustable to make the seat the most appropriate in terms of convenience and a holding ability for the passenger using the seat.