An apparatus for automatically treating the excrement comprises a mounting unit, a control device unit, and a washing water supply path which is connected from the washing water supply part to the mounting unit. The washing water supply part comprises a washing water storage tank in which the washing water is stored. A pump is operated in a forward or in a reverse direction to supply the washing water of the washing water storage tank to the mounting unit, or collecting the residual washing water in the washing water supply path to the washing water storage tank. An instantaneous water heater provides on the washing water supply path to heat the washing water a control portion which controls the operations of the pump in the forward direction or the reverse direction.