To reduce the stock numbers by arranging a water quantity adjusting device on the inlet side of a branched resupply water pipe for supplying water to a low tank, and applying one kind of ball tap to both toilet bowls of a siphon type or a washing-off type.

A float 12 is connected to an arm fixing cap 10 of a ball tap 9 via an arm 11 so that this float 12 closes the ball tap 9 by the rise of a water level of wash water stored in a main body part 2. A resupply water pipe 13 is connected to the arm fixing cap 10 via a connecting pipe having a water quantity adjusting ring and projecting outward in a branch shape, and an overflow pipe 13 is connected to the tip. Waste water is brained into a toilet bowl from a waste port 5 by pulling up a ball valve 1 by operating a lever 7. A washing-off type toilet bowl is used by stopping supply water to the resupply water pipe 13 side by fastening an adjusting ring. Thus, one kind of ball tap 9 can be applied to a siphon type and a washing-off type to reduce the stock numbers to reduce a cost.