PURPOSE: To improve efficiency of a steam generator and to enable a steam generating pipe of the steam generator to have a pumping function by constituting the steam generating pipe into a double pipe wherein an inner pipe thereof having one end sealed to an outer pipe serves as a liquid inlet pipe.

CONSTITUTION: A heat collector plate 10 is disposed inclined so that it may be shined substantially perpendicularly by heat radiation 11 of the sun. The heat collector plate 10 has a steam generating pipe 12 secured thereto which has a liquid inlet pipe 13 inserted therein from below. The lower end of the outer pipe is sealed to the liquid inlet pipe 13, that is, an inner pipe. The upper end of the outer pipe terminates into a steam outlet pipe 14. The upper end of the liquid inlet pipe 13 is provided with an opening 15 disposed adjacent to the upper end of the outer pipe.