1. An electronic component mounting board comprising:a circuit board having (1) a wiring layer that includes a first insulating layer, a second insulating layer, and a conductor layer between the first insulating layer and the second insulating layer and (2) a recess in a main surface of one side of the circuit board, the main surface being on a same side of the conductor layer as the first insulating layer;
a passive component located in the recess;
an active component arranged above the passive component and the main surface of the one side of the circuit board and connected to the passive component; and
a shield layer formed of a material containing a magnetic material and provided between a bottom surface of the recess and a lower surface of the passive component;
wherein the recess extends through the first insulating layer and the conductor layer such that the bottom surface of the recess is the second insulating layer.