An expander of the invention includes: n-number of rotary type fluid mechanisms (where n is an integer equal to or greater than 2), a first suction port (41b) for sucking a working fluid into a suction-side space (55a) of a first fluid mechanism (41), a communication port (43a) connecting a discharge-side space (55b) of a k-th fluid mechanism (where k is an integer from 1 to n−1) and a (k+1)-th suction-side space (56a) to form a single space, and a discharge port (51a) for discharging the working fluid from the discharge-side space of an n-th fluid mechanism. The expander further includes a second suction port (72f) being capable of changing its connecting position to the suction-side space (55a) of the first fluid mechanism (41), for sucking the working fluid into the suction-side space (55a).