A fabricating method according to the present disclosure is a component built-in multilayer substrate fabricating method for incorporating a component (12) in a resin multilayer substrate (11) formed by laminating and pressing thermoplastic resin sheets (111a to 111d) so as to crimp them to each other. With the fabricating method according to the present disclosure, a metal pattern (13) is provided on a component mounting surface of the thermoplastic resin sheet (111a). Further, the component (12) is inserted in the area sandwiched by the metal pattern (13). Out of widths relating to the area sandwiched by the metal pattern (13), the width in the component mounting surface side is assumed to be a width W2, and the width in the component-insertion side is assumed to be a width W3, the width W2 being equal to or larger than a width W1 of the component but less than the width W3.