A rotary type expansion machine (60) is provided with two rotary mechanisms (70, 80). The first rotary mechanism (70) has a displacement volume smaller than that of the second rotary mechanism (80). The first low pressure chamber (74) of the first rotary mechanism (70) and the second high pressure chamber (83) of the second rotary mechanism (80) are connected by a communication passage (64) to constitute a single expansion chamber (66). A high pressure refrigerant introduced into the first rotary mechanism (70) expands in the expansion chamber (66). The communication passage (64) has an injection passage (37) connected thereto. When a solenoid valve (90) is opened, the high pressure refrigerant is introduced into the expansion chamber (66) also from the injection passage (37). Thereby, a lowering of power recovery efficiency is suppressed even under conditions where the actual expansion ratio is smaller than the designed expansion ratio.
