Patent ID: 7794017

Claim:
A chair comprising: a seat; a seat receiving member supporting the seat, the seat receiving member being configured to move the seat at least one of downward and rearward in response to a person being seated on the seat; a backrest including a lumbar support portion that supports the lumbar of the seated person at a lower portion of the backrest; and a cooperative moving unit configured to forwardly move the lumbar support portion of the backrest in response to at least one of the downward and rearward movement of the seat, wherein the backrest is flexible to deform in a side view and a plane view by being pressed by the seated person; an upper portion of the back rest being connected to a back supporter, the lumbar support portion being connected to the cooperative moving unit; the lumbar support portion is moved forwardly and rearwardly by inclining the backrest centering on the upper portion of the back rest in a side view thereof; and the backrest includes a back plate formed of a synthetic resin including an elastomer, and a plurality of vertically prolonged ribs are formed at one of a front face, a rear face, and both the front and the rear face of the back plate.