A lightweight, mobile friction stir welding machine, a sticking pad for the friction stir welding machine, and a friction stir welding system are provided. The sticking pad 46 has a flat base member 51 facing an object, an annular sealing member 52 protruding from one of major surfaces of the base member 51 so as to surround a central area of the surface of the base member 51, a slippery member 53 attached to the end surface of the annular sealing member 52 facing the object, and one or some deformation-suppressing protrusions 56 protruding from the surface facing the object of the base member 51. The slippery member 53 is made of a material that can make the slippery member 53 contact the object with a friction coefficient lower than that with which the sealing member 52 can be in contact with the same object.
