Power generation apparatus

A power generation apparatus comprising:

• an evaporator that causes a liquid working medium to be evaporated by application of heat from a thermal medium;
• an expander that expands a gas of the working medium to produce power in said expander, said expander being a positive displacement expander;
• a condenser that causes the working medium to be condensed by cooling the gas of the working medium with a coolant medium;
• a positive displacement circulating pump that circulates the working medium;
• a closed-loop circulating channel in which said evaporator, said expander, said condenser, and said circulating pump are connected in series;
• a condensing pressure detector that detects a condensing pressure in said condenser, and
• a controller that controls a rotational speed of said circulating pump and a suction volume of said expander, wherein the controller comprises means for increasing the rotational speed of said circulating pump and the suction volume of said expander as the condensing pressure detected by said condensing pressure detector increases.