In a first step, a circuit sheet is set such that a first region of a second main surface of the circuit sheet is in contact with a plateau portion of a first mold and a second region is not in contact with the first mold. In the first step, a first fixed portion of the circuit sheet is arranged on a first portion of the first mold, and a second fixed portion is arranged on a second portion of the first mold. The first portion is a portion that is higher than the plateau portion and runs along at least one of a first protruding portion and a second protruding portion provided along the plateau portion. The second portion is a portion where the first protruding portion or the second protruding portion is not provided along the plateau portion.