A flush toilet apparatus includes a toilet body that includes a rim water spout port, a tank that stores washing water, a rim side water supply channel that supplies washing water to the rim water spout port, a tank side water supply channel that supplies washing water to the tank, a flow channel switching part that adjusts an amount of washing water that is supplied to one or both of the rim side water supply channel and the tank side water supply channel, and an electrical power failure detection part that detects electrical power failure, wherein, in a case where electrical power failure is caused when washing water is supplied to the tank side water supply channel, the flow channel switching part decreases washing water that is supplied to the tank side water supply channel and increases washing water that is supplied to the rim side water supply channel.