The invention relates to a thermo-pneumatic actuator having a cavity defined by walls and being hermetically sealed, which is inflated with a working medium that alters the gas pressure thereof when a temperature change occurs. A wall region of the cavity is constructed as a ductile membrane, which can be deflected in at least two working positions located on both sides of a neutral position, in which the membrane is curved in opposite directions to one another. In order to alter the gas pressure in the cavity, and to adjust the membrane from one working position to the other working position, a tempering device is heat-conductively connected to the working medium. In the neutral position, the membrane is compressively loaded such that respectively, it maintains its position in both working positions if no outside force impacts the membrane.