This aims to provide solar heat collecting means for conserving energy while requiring no motive power, for lowering the cost by simplifying the constitution and for acquiring a high recovery temperature even in winter. Disclosed is a heat collecting apparatus comprising a closed circuit (1), in which a working fluid (as will be called the CO2 fluid) composed mainly of CO2 circulates, a heat collector (2) for collecting heat in the CO2 fluid, and a heat exchanger (3) for recovering the heat from the heat-collected CO2 fluid. The heat exchanger (3) liquidizes the CO2 fluid (w) by recovering the reserved heat, and generates a liquid head pressure (H) of the CO2 fluid (w) on the exit side by establishing a level difference between the entrance side, into which the CO2 fluid (w) flows, and the exit side, from which the CO2 fluid (w) flows. The heat collector (2) is disposed in the closed circuit (1), and collects the heat in the liquidized CO2 fluid (w) thereby to bring the CO2 fluid (w) on the exit side into a supercritical state. The heat collecting apparatus is constituted to establish a natural circulation of the CO2 fluid (w) in the closed circuit (1).