A fiber crimping apparatus is disclosed which has an internally contacting type nip roller which consists of a ring roller and an inscribed roller rotating together in the same direction at the same speed. The apparatus is provided with a control groove formed on the surfaces of the ring roller and/or the inscribed roller holding the fiber bundle between them and which controls the thickness in the transverse direction of the fiber bundle to be crimped. As the fiber bundle in the nip zone is controlled in the transverse direction, the constriction of the fiber bundle is produced evenly in full width and the crimping process produces even waves and the apparatus is operated stably.