A chair comprising: a base supported by a leg unit; a seat over the base; a pivot shaft pivotally mounted to the base transversely of the chair; a backrest fixed at a front end to the pivot shaft and standing at a rear end of the seat, the backrest turning between an upright position where the backrest is upright and a rearward-inclined position where the backrest is inclined rearward around an axis of the pivot shaft; a rotary member 16 fixed at a proximal end to the pivot shaft; a biasing-force transmitting member pivotally mounted at a proximal end to an eccentric portion of the rotary member via a shaft; biasing means (20,40) disposed between the biasing-force transmitting member and part of the base and storing a reaction force by compression; a fulcrum member in the base, the fulcrum member being capable of coming in contact with a middle of a pressed side of the biasing-force transmitting member and of moving along the pressed side; and a moving member moving the fulcrum member along the pressed side of the biasing-force transmitting member, wherein the biasing-force transmitting member acts as a lever having a contact portion with the fulcrum member as fulcrum to reverse a biasing force of the biasing means (20,40) acting on a distal end as a point of effort whereby the proximal end as a point of action biases the rotary member in a direction where the backrest stands up, characterized in that: when the backrest is upright, the fulcrum member is spaced from the pressed side of the biasing-force transmitting member or is in contact with the pressed side so that a biasing force of the biasing means (20,40) does not act on the fulcrum member. a base supported by a leg unit; a seat over the base; a pivot shaft pivotally mounted to the base transversely of the chair; a backrest fixed at a front end to the pivot shaft and standing at a rear end of the seat, the backrest turning between an upright position where the backrest is upright and a rearward-inclined position where the backrest is inclined rearward around an axis of the pivot shaft; a rotary member 16 fixed at a proximal end to the pivot shaft; a biasing-force transmitting member pivotally mounted at a proximal end to an eccentric portion of the rotary member via a shaft; biasing means (20,40) disposed between the biasing-force transmitting member and part of the base and storing a reaction force by compression; a fulcrum member in the base, the fulcrum member being capable of coming in contact with a middle of a pressed side of the biasing-force transmitting member and of moving along the pressed side; and a moving member moving the fulcrum member along the pressed side of the biasing-force transmitting member, wherein the biasing-force transmitting member acts as a lever having a contact portion with the fulcrum member as fulcrum to reverse a biasing force of the biasing means (20,40) acting on a distal end as a point of effort whereby the proximal end as a point of action biases the rotary member in a direction where the backrest stands up, characterized in that: when the backrest is upright, the fulcrum member is spaced from the pressed side of the biasing-force transmitting member or is in contact with the pressed side so that a biasing force of the biasing means (20,40) does not act on the fulcrum member.