To solve problems in a conventional system wherein the diversification of cargo in recent years resulted in loading cargo of phenol or the like which must avoid heating of 100°C or higher although heating is necessary, so that a warm water heating device of a low temperature heat medium is separately equipped as a heating device for a cargo tank in addition to steam heating of a high temperature heat medium, and warm water and steam are changed over for use at a header part of an upper deck, but a pump chamber has a washing warm water heating device which is the almost same device although the capacity is different to some extent, as a tank cleaning device to produce warm water by heat- exchanging with steam which causes a sense of double facilities and a problem of installation as it is installed in a limited space and the separate equipment has turned into excess equipment from the viewpoint of the frequency of warm water heating.

The warm water heating device using warm water of the low temperature heat medium in addition to the steam of a standing high temperature heat medium is used also as the washing warm water heating device, and according to an application, warm water produced in a pump chamber PR is connected to a heating coil 7, a deck heat exchanger 24 or a butterworth machine 2 at an upper deck UD to heat or insulate cargo or to wash a cargo tank.