The valve (10) has a seat valve (27) with a hollow cone shaped valve seat (24) and a hemispherical closing member (26). A feed bore hole (23) leads centrically into the valve seat (24), said bore hole being connected to a pressure medium inlet (19). A magnet armature (30) which has an opening effect on the seat valve (27) engages with a tappet (25) which comprises the closing member (26).The magnet armature cooperates with a pole core (42) according to the flat armature principle. A pre-stressed readjusting spring (39) which has a closing effect on the seat valve (27) is arranged between the pole core (42) and the magnet armature (30). The valve (10) works as a proportional valve because the magnetic force, in addition to the suitable design of the seat valve (27) and the tappet (25), can be modified in a continuously adjustable manner, and together with the hydraulic force, has a form which increases monotonically as the valve-opening lift increases, while the resistance of the spring - which also increases monotonically as the valve-opening lift increases - has a positive increase which is greater than the positive increase of the magnetic or hydraulic force characteristic.