PURPOSE: To facilitate handling of the titled apparatus and the mounting operation thereof on a roof, and to make it possible to simply carry out the repair thereof by making it possible to easily separate a heat collecting part comprising a heat collector and a heat receiving tank and a hot water storage part comprising a hot water tank.

CONSTITUTION: An outer box 4 contains therein a heat pipe type heat collector 5, and an enclosed vessel type heat receiving tank 6 mounted on the upper surface of a condensing part 5a of a heat collector 5 and further having a metal bottom plate 17, and a hot water storage tank 22 is placed on the upper surface of the heat receiving tank 6 by way of a heat insulating material 7, and further the heat receiving tank 6 and the hot water storage tank 22 are mutually communicated with each other by means of an outgoing connecting pipe 24 and an incoming connecting pipe 25. As a result, the heat collecting part 2 can be easily separated from the hot water storage part 3, and the handling of the apparatus and the mounting operating on the roof can be easily carried out and the repair thereof can also be carried out easily. In addition, the packaging and the transport thereof are also easy, and a small number of housing places may be sufficient and furthermore, heat loss due to heat discharge at nighttime may be extremely small.