A sheet thickness detector incorporated in a sheet conveyor and/or an image forming apparatus includes multiple first rollers aligned in a direction perpendicular to a sheet conveying direction, multiple second rollers facing the respective first rollers, a first roller shaft supporting two first rollers, at least one second roller shaft supporting rollers other than the two first rollers, at least one third roller shaft to support at least three second rollers, a first roller shaft holder supporting the first roller shaft to move from the at least one third roller shaft in a contact/separation direction, a biasing member biasing the first roller shaft toward at least one third roller shaft, and a displacement amount detector detecting an amount of displacement of the first roller shaft. A thickness of a sheet between the first and second rollers is detected based on a detection result by the displacement amount detector.