A component built-in substrate incorporates a chip capacitor in a multilayer substrate including laminated base material layers made of thermoplastic resin. The chip capacitor includes an uneven portion including a recessed portion and a projected portion on one side in a laminated direction. On one side of the chip capacitor in the multilayer substrate, a density of low fluid member with a melting point higher than a fluidization temperature of the base material layers is higher in a region overlapping the recessed portion of the chip capacitor than in a region overlapping the projected portion of the chip capacitor when viewed in the lamination direction.