To provide a case enclosed type feed water system facilitating feed water pump attaching/detaching work without being influenced by water flowing out of the interior of the pump.

A plate-like installation base 12 elastically supported by elastic members 11 is provided in a box type case 1 with the front side opened and with the rest closed. A pump base 15 with the whole periphery surrounded by a weir 19 is attached to the lower part of a feed water pump 2. After the feed water pump 2 is placed on the upper face of the installation base 12 through an opening part 1a and enclosed in the case 1, only a base part facing the opening side of the pump base 15 is fixed to a shelf part 5 by bolts 23. Fitting of the feed water pump 2 is therefore completed without needing work on the inner side opposite to the opening side of the case 1, and at the time of detaching the feed water pump 2, even though water flows out of the interior of the pump, this water is stopped by the weir 19 so as to prevent the water from splashing on a worker.