A joining member for joining parts or materials to form a joined structure is constituted by a composite material containing a heating assistant in a matrix material. For disintegrating the joined structure, it is placed in a heating zone, and a high frequency magnetic field or a high frequency electric field, or a high frequency magnetic field and a high frequency electric field are applied to the joining member. The heating assistant may be in a form of a particle or a fiber containing at least one of a soft magnetic material, an electrically conducting material and a dielectric material. The matrix material may be plastic or ceramic. The disintegration of the joined structure can be efficiently and selectively carried out, thus contributing to efficient recycling.