To make a rocks water preparation device for one of fuctional waters smaller, lighter in weight and lower in price.

Rocks liquid 3 of given volume is mixed into tap water 2 of given volume or the like, and an open case 4 filled with active carbon formed into the trumpet shape so that the filtration area of a replacement glass filter paper 7 is enlarged is fixed on a lower tap main stopcock 6 in a plastic water tank 5 placed on the lower section, and the replacement glass filter paper 7 and a glass fiber filter paper protective net 9 together with a glass fiber filter paper cover 14 are fixed on a filter cylinder 8 with a protruded screw on the outside by a fixing nut 12. Filtered rocks water is prepared by opening and closing the lower tap. The glass fiber filter paper 7 can be replaced simply and easily.