PURPOSE: To provide a washing device of a floor surface wash robot, which presents a high washing efficiency during service, is capable of passing a narrow place when it is out of service, and with which maintenance for the washing mechanism can be done easily.

CONSTITUTION: A floor surface wash robot is so structured that a washing mechanism 13 to wash the floor surface while touching it directly is mounted on the robot body 1 which runs on the floor surface to be washed, wherein the washing mechanisms 13 is borne by the robot body 1 with the aid of a supporting mechanism 2, is rotatable between the washing attitude generating a width greater than the crosswise width of the body 1 and the maintenance attitude with the crosswise width shrunk upon having 90 deg. rotated in a vertical plane perpendicularly intersecting the robot advancing direction, and can be locked and unlocked in/from the washing attitude and maintenance attitude by a locking mechanism installed in linkage with the supporting mechanism 2.