Abstract: A closing unit of an injection molding machine includes a moveable mold mounting plate and a fixed mold mounting plate, a hydraulic pressure mechanism for building up a closing pressure, at least one column provided with an external profile, and at least one two-part nut which is provided with an internal profile and the halves of which are coupled in motionally opposite relationship. The at least one column in the closed condition of the two-part nut is lockable by a positively locking relationship between the internal profile and the external profile relative to the moveable mold mounting plate or relative to the pressure mechanism. There is also provided an electric drive for opening and closing the two-part nut.