A chair in which a biasing force acting on a back can be changed even if the stroke of a moving member is small, thereby enabling the device to be compact, and the biasing force can be steplessly adjusted with light force. A biasing force transmission member (41) reverses the biasing force of a biasing mechanism acting on a tip portion of the biasing force transmission member (41) which is a point of effort (Q) with a point abutting a fulcrum member (49) working as a fulcrum (P) for a lever, transmits the biasing force to a base end of the biasing force transmission member (41) which is a point load (R) to bias the back in an upright direction, and moves the fulcrum member (49) along a side edge of the biasing force transmission member (41) on a pressure receiving side to be able to adjust the biasing force.