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 has a flat base member facing an object, an annular sealing member protruding from one of major surfaces of the base member so as to surround a central area of the surface of the base member, a slippery member attached to the end surface of the annular sealing member facing the object, and one or some deformation-suppressing protrusions protruding from the surface facing the object of the base member. The slippery member is made of a material that can make the slippery member contact the object with a friction coefficient lower than that with which the sealing member can be in contact with the same object.