A method for joining two substances and device for joining two substances are suited for practical use and significantly reduce the difficulty of accurately forming the focal formation position of an ultrashort pulse laser in a case of joining substances with use of a nonlinear absorption phenomenon, as well as a joined body and a manufacturing method for the for the same. Provided is a method for joining two substances by causing a nonlinear absorption phenomenon to occur with use of an ultrashort pulse laser beam. Among the two substances, a first substance that is positioned on a side on which the ultrashort pulse laser beam is incident is composed of a transparent material, and the two substances are joined by generating, at a joining face of the two substances, a filament area that is generated by a self-focusing effect of the ultrashort pulse laser beam in the first substance.