The intention is to provide an actuator which makes it possible to change the opening time and to manually lock the supply of gas. For this purpose, the actuator consists of a housing (9) which is closed by a cover (10). A working diaphragm (8) is clamped between the housing (9) and the cover (10) and subdivides a space enclosed by the housing (9) and the cover (10) into a working pressure chamber (11) and an outlet pressure chamber (13). A lever (15) which is supported on the working diaphragm (8) and acts on a gas valve (2) via a drive plunger (16) is pivotably mounted in the housing (9). The actuator also has an adjustable pressure control valve (6) and a solenoid valve (7). When an inlet pressure line (12) is closed, the solenoid valve (7) opens a connecting channel (28) between the working pressure chamber (11) and the outlet pressure chamber (13). In contrast, in the open position, the inlet pressure line (12) is connected to the working pressure chamber (11) and to the pressure chamber (21). A throttle (29) in the inlet pressure line (12) upstream of the solenoid valve (7) makes it possible to manually set the opening cross section of the inlet pressure line (12).