Flush water tank apparatus and flush toilet apparatus provided with the same

A flush water tank apparatus configured to supply flush water to a flush toilet, comprising:

• a reservoir tank configured to store the flush water to be supplied to the flush toilet and having a discharge port formed to discharge the stored flush water to the flush toilet;
• a discharge valve configured to open and close the discharge port to supply the flush water to the flush toilet and to stop a supply of the flush water to the flush toilet;
• a discharge valve hydraulic drive portion configured to drive the discharge valve using a water supply pressure of the supplied water;
• and
• a discharge/vacuum break valve device provided on an upstream side of the discharge valve hydraulic drive portion and configured to supply the water supplied from the upstream side to the discharge valve hydraulic drive portion on a downstream side,
• wherein the discharge valve hydraulic drive portion includes:
• a cylinder into which the water supplied through the discharge/vacuum break valve device flows;
• and
• a piston that is slidably disposed in the cylinder, and is configured to be moved by a pressure of the water flowing into the cylinder, lifting the discharge valve with a force based on the pressure of the water supplied through the discharge/vacuum break valve device, and
• wherein the discharge/vacuum break valve device includes:
• a valve body that operates, when the supply of the water from the upstream side is stopped, to discharge the water flowing backward from the discharge valve hydraulic drive portion simultaneously with opening the upstream side of the discharge/vacuum break valve device to an atmosphere.