The invention discloses a flattening device, comprising an installation rack and a plurality of clamps which are installed on the installation rack for fixedly clamping the plate-shaped objects. The clamps are arranged on the installation rack through a plurality of flattening structures; at least one bidirectional flattening structure is among the flattening structures; the bidirectional flattening structure can drive the clamps to produce displacements or displacement components which are in the transverse direction and a longitudinal direction which are perpendicular to each other to apply the transverse direction pulling force and the longitudinal direction pulling force or the transverse direction pulling force component or the longitudinal direction pulling force on the plate-shaped body in the meantime. The flattening device disclosed by the invention is provided with the bidirectional flattening structure to drive the clamps to perform the displacements or the displacement components in two perpendicular directions which are the transverse direction and the vertical direction, and the plate-shaped object is under the action of the two pulling forces or the two pulling force component which are perpendicular to each other, so that the plate-shaped object is flattened in the transverse direction and the vertical direction, and the flatness of the plate-shaped object is guaranteed.