To provide a small-sized opening and closing device for the seat or lid of a toilet stool.

A seat lid opening and closing device is composed of a bracket mounted on the body of water closet, rotary cylinder 5 attached to the bracket, a pair of mounting parts for seat and lid, a shaft 8 with one end engaged with the bracket in such a way as penetrating the rotary cylinder, a rotary cam 9 engaged in the cylinder, a slide cam 10 mounted slidably in the axial direction of the shaft, a damper ring holder 11 attached slidably in the axial direction of the shaft, an adjusting nut 15 screwed fast in contact with the damper ring holder, and a damper ring 12 installed in the area to the inner wall of the rotary cylinder. The arrangement may include an adjusting cap 4 installed in such a way as put on the adjusting nut and rotatable together with it and an 0-ring installed in such a way as coiled on the damper ring holder.