A mounting structure includes a circuit board including one principal surface on which a multilayer capacitor is mounted. The circuit board includes a first insulating layer, and a second insulating layer having a Young's modulus smaller than that of the first insulating layer. The second insulating layer is closer to the one principal surface than the first insulating layer. A multilayer capacitor built-in substrate includes a circuit board, a multilayer capacitor on one principal surface of the circuit board, and a resin layer on the one principal surface of the circuit board and embedding the multilayer capacitor. The circuit board includes a first insulating layer, and a second insulating layer having a Young's modulus smaller than that of the first insulating layer. The second insulating layer is closer to the one principal surface than the first insulating layer.