The sheet thickness detector includes a fixed member, a displacement roller disposed opposite the fixed member and movable in such a linear direction as to be contacted with or separated from the fixed member when the sheet passes through a nip therebetween, bearings rotatably supporting a shaft of the displacement roller, a displacement member movable in the linear direction in conjunction with the displacement roller and integrated with at least one of the bearings, and a displacement sensor operatively connected to the displacement member and detecting displacement of the displacement member. The thickness of the sheet passing through the nip is determined based on the amount of displacement of the displacement member.