Heat-receiving pipes (23) of a heat receiver (10) have portions (K) having high heat flux on at the side near an opening (11b) in a length direction and extending to positions outside of a casing (11) in a radial direction. Expanded sections (20c) having an expanded pitch circle diameter (D) constituted by the plurality of heat-receiving pipes (23) are formed, and a heat input quantity per unit area of the heat-receiving pipe (23) is decreased in the portions (K) near the opening (11b).
