An object of the present invention is to provide a functional device-embedded substrate that can be thinned and suppress occurrence of warpage. The present invention provides a functional device-embedded substrate including at least a functional device including an electrode terminal, and a covering insulating layer covering at least an electrode terminal surface and a side surface of the functional device, the functional device-embedded substrate including a first pillar structure around the functional device inside the covering insulating layer, the first pillar structure including a material having a thermal expansion coefficient between thermal expansion coefficients of the functional device and the covering insulating layer, wherein the first pillar structure is arranged at a position where a shortest distance from a side surface of the functional device to a side surface of the first pillar structure is smaller than a thickness of the functional device.