A chair equipped with a lumbar support unit is disclosed. The lumbar support unit includes a lumbar plate attached to a lower portion of a tiltable backrest part, and an actuating connector comprising a connecting wire which is connected at one end to an upper end of the lumbar plate and is connected at the other end to a chair frame supporting the seat and back parts, and a connecting tube surrounding the connecting wire, which is positioned at one end at a location downwardly spaced from the one end of the connecting wire, and is connected at the other end to a movable frame. The lumbar plate is automatically protruded forward to snugly support a lumbar region of a user when the back part is tilted rearwardly. The chair can afford convenient operation and protection of a lumbar region of a user.