The invention relates to a proportional valve (1), having a pilot control valve (2) that can be controlled by means of a control signal and having a booster valve (3) that can be actuated by means of the pilot control valve (2). The proportional valve (1) has a compressed-air connection (6) for connecting a compressed-air supply, a working connection (5), and an air-removal connection (4). The booster valve (3) has three valve elements (8, 9, 10), which are arranged one after the other and can each be moved in an axial direction against a spring force. In a base position of the proportional valve (1), the first, second, and third valve elements (8, 9, 10) are spaced apart from each other in pairs, and, within the booster valve (3), a first sealing seat (26) effective between the first valve element (8) and the second valve element (9) and a second sealing seat (27) effective between the third valve element (10) and the housing (16) are designed and arranged in such a way that, when the control signal that controls the pilot control valve (2) is varied and an adjustment of the axial positions of the first, second, and third valve elements (8, 9, 10) is caused thereby in a cascaded manner, different switching states for removing air from and supplying air to the working connection (5) and for holding a pressure present at the working connection (5) can be set. Furthermore, a position sensor (31) that senses the axial position of the first valve element (8) is provided and a control unit (36) of the proportional valve (1) is designed in such a way that the measurement signal of the position sensor (31) is evaluated in order to calculate the control signal for the pilot control valve (2) that is required to achieve a desired switching state of the booster valve (2).