To provide equipment for tilting a back of a chair which has enough strength when assembled and can be disassembled easily to sort out parts for disposal though a spring unit, which applies a force to a part supporting a seatback elastically to tilt it forward for an attaching part mounted on a leg, can be assembled easily.

A spring unit, which applies a force to a part supporting a seatback elastically, has a structure that a metallic, tension rod 44 is screwed in a knob 43 made of a synthetic resin. A screwing shaft 48, made on a base of the tension rod, and a nut 49 with a long flange 50 are screwed together. A long, attaching hole 51, which has the same shape as the flange and can pass through the flange, is made on the knob. The nut is penetrated from the inner side of the attaching hole made on the knob. The nut is turned 90 degrees, and the flange is caught at the outer side of the attaching hole. A pair of leg pieces 53, placed on a cap 52 which conceals the screwing shaft, are joined to and caught to the remaining parts at both sides of the flange in the attaching hole.