A chair includes: a leg body; a backrest supporting body supported by the leg body; a backrest rear supporting member supported by the backrest supporting body; and a backrest that is supported by the backrest rear supporting member and supports the back of a user. The backrest has: a flexible upholstering material configured to receive the back of the user and is displaceable depending on the back; and a pair of vertical frame sections that are mounted on the upholstering material, have lower ends connected to the back rest rear section support section, and are separated in a width direction in which twisting deformation is allowed depending on a force applied from the upholstering material.