To provide an automatic defecation disposal system which can realize the accurate discharge of filth and washing operation while reducing burden in a prolonged wearing by enabling the automatic positioning of a diaperlike casing with a human body to match the difference in the physical type of a patient with a simple structure.

In the automatic defecation disposal system K with the diaperlike casing A, the diaperlike casing A has a support plate part 100, an erected part 200 and a fixing means for the positioning of the diaperlike casing A with the human body. The support plate part 100 has a filth passage 101 and a discharge part 102. The erected part 200 has a front recessed part and the fixing means has an expansible/retractable member so soft as to abut on the human body and a pump 400 for adjusting the volume of the expansible/retractable member 210. The volume of the expansible/retractable member 210 is increased with the pump 400, thereby pressing the human body with the expansible/retractable member 210.