Provided is a substrate with a built-in electronic component that can minimize an occurrence of a deformation such as warping or distortion of the substrate with a built-in electronic component, which is caused by a difference in rigidity between a region of low rigidity and a region of high rigidity that are formed in a core layer thereof. In the substrate with a built-in electronic component, electronic components 12 are respectively housed in a plurality of housing portions 11a1 that are formed in a core layer 11a, and in the core layer 11a, a plurality of openings 11a2 filled with an insulator 11k are formed.