In a solar heat powered plant according to the present invention, hot water is normally circulated through a hot-water tank, a low-temperature-side heat load unit, a return tank, a low-temperature-side heat exchanger, and again through the hot-water tank, in the order named, under the condition in which first and second valves are opened and closed, respectively. On the other hand, in warming up the hot-water tank, the first and second valves are closed and opened, respectively, so that the hot water is circulated between the hot-after tank and the low-temperature-side heat exchanger, through a by-pass pipe. Thus, the warming up of the hot-water tank can be achieved in a short time.