A pressure controlling and/or regulating device (8) for a fluid medium, in particular air or gas, but preferably nitrogen, to be supplied besides the plastic molten mass to an injection molding tool, may be designed as a stationary, but preferably as a mobile unit, arranged between a pressure generator/accumulator (7) and an injection system associated to the injection molding tool (3), for example in a nozzle head or in a supplementary module. The device has a main line (21) that leads from the pressure generator/accumulator (7) to the injection system (27) and which can be switched by a valve control only between letting through or blocking the inflow of medium, a first bypass line (28) to a receiving side of a pressure sensor (29) whose other receiving side is sensitive to the medium pressure in the injection molding tool, and a second bypass line (30) which can be switched by a valve control influenced by the pressure sensor (29) between a letting through or a blocking state, forming an outflow of medium from the injection molding tool, in particular a medium return flow to the pressure generator/accumlator (7). The essential trait of this invention is that the main line (21) consists in sections of at least two parallel flow paths (23a and 23b); each flow path (23a and 23b) is equipped with a medium inflow control valve (24a and 24b) which can be selectively switched between a letting through or a blocking state, the medium inflow control valves (24a and 24b) have different openings (25a, 25b) and can be progressively switched individually and/or together between a letting through or blocking state depending on the pressure difference detected at the pressure sensor (29).