Abstract: The invention relates to a method for converting thermal energy into mechanical work. Said method comprises the following steps which are performed as a cycle: A liquid work medium is fed from a supply reservoir (1) to a work container (3); the work medium in the work container (3) is heated by a first heat exchanger (5); a sub-amount of the work medium flows from the work container (3) to a pneumatic-hydraulic-converter (8), a hydraulic medium from the pneumatic-hydraulic-converter (8) is compressed in a work machine (9) in order to convert the hydraulic work of the hydraulic medium into mechanical work; the work medium from the pneumatic-hydraulic-converter (8) is fed back into the supply reservoir (1) and the hydraulic medium is returned into the pneumatic-hydraulic-converter (8). The invention also relates to a device for carrying out said method.