Expander and heat pump using the expander

An expander comprising:

• n-number of rotary type expansion mechanisms (where “n” is an integer equal to or greater than 2) each having a cylinder, a shaft with an eccentric portion, a piston fitted to the eccentric portion and rotating eccentrically in the cylinder, and a partition member partitioning a space between the cylinder and the piston into a suction-side space and a discharge-side space;
• a first suction port for sucking a working fluid into the suction-side space of the first expansion mechanism;
• a communication port connecting the discharge-side space of the k-th expansion mechanism (where “k” is an integer from 1 to n−1) and the suction-side space of the (k+1)-th expansion mechanism to form a single space;
• a discharge port for discharging the working fluid from the discharge-side space of the n-th expansion mechanism;
• and
• a second suction port for sucking the working fluid into the suction-side space of the first expansion mechanism, the second suction port being capable of changing its connecting position to the suction-side space of the first expansion mechanism.