A component built-in substrate includes a multilayer body and a substrate including a multilayer ceramic electronic component embedded therein. The multilayer ceramic electronic component includes a first connection portion that protrudes from the first external electrode, and a second connection portion that protrudes from the second external electrode. The substrate includes a core material. The multilayer ceramic electronic component including the first connection portion and the second connection portion includes a surface covered by the core material and embedded in the substrate. The first connection portion protrudes toward a surface of the substrate, and is not exposed at the surface of the substrate. The second connection portion protrudes toward the surface of the substrate, and is not exposed at the surface of the substrate.