A method for manufacturing a board with a built-in electronic element, includes providing a support substrate including a support base and a metal foil, forming a protective film made of a metal material on the metal foil of the support substrate, forming a conductive pattern made of a metal material on the protective film by an additive method, placing an electronic element on the support substrate with the conductive pattern such that a surface of the electronic element where a circuit is formed faces the conductive pattern, covering the electronic element with an insulative resin, etching away the metal foil using a first etching solution such that the protective film is not dissolved by the first etching solution or that the protective film has an etching speed which is slower than an etching speed of the metal foil, and electrically connecting terminals of the electronic element and a part of the conductive pattern.