In a built-in-coil substrate, when viewed in perspective in a stacking direction in which insulating layers of a substrate body are stacked, mutually superposed second coil elements are located further inward than inner peripheries of mutually superposed first coil elements. A cavity is continuous between at least one of the second coil elements and one insulating layer that is in contact with the second coil element(s), and another insulating layer that opposes the second coil element(s) such that the second coil element(s) are exposed, and, when viewed in perspective in the stacking direction, the cavities have annular shapes and extend further inward than the outer peripheries of the mutually superposed first coil elements, there being an interval provided between the cavities and these outer peripheries, and further outward than the inner peripheries of the mutually superposed second coil elements.