A clamping unit includes two fixed platens, kept at a distance by tie bars, a platen which can be displaced in relation to the fixed platens, part of an injection mold respectively being arranged on one of the fixed platens and on the displaceable platen, a force generating element to be arranged between the one fixed platen and the displaceable platen, and the tie bars being arranged in vertical alignment. The force generating element is fastened to the displaceable platen and that on the one fixed platen there is arranged a locking element which forms a stop for the force generating element on the one fixed platen or exposes an opening for at least part of the force generating element to enter or pass through the one fixed platen.