A pressure reducer includes a housing with an axially displaceable biased control body in order to close a connection between an inlet and an expansion chamber, where the housing is equipped with an axially displaceable biased actuating piston in order to displace the control body against the spring load of the control body as a function of the pressure in the expansion chamber and to open the connection, the housing being made of plastic, and the pressure reducer includes a separately made insert, where the insert is fixed between the inlet and the expansion chamber in the plastic housing and said insert has a guide bore, which is connected to the inlet and supports the control body, and a connecting bore, which adjoins the guide bore and which opens into the expansion chamber, where the insert forms an annular shoulder surface between the connecting bore and the guide bore, said shoulder surface interacting as a seating surface with the seal on the control body.