An electronic component built-in module according to the present invention includes a pair of opposed circuit substrates, each of which includes a wiring pattern and an insulating base material containing a resin, an insulating layer that is placed between the pair of circuit substrates and contains an inorganic filler and a resin composition containing a thermosetting resin, an electronic component that is embedded in the insulating layer, and an inner via that is provided in the insulating layer so as to make an electrical connection between wiring patterns provided on different circuit substrates. A glass transition temperature Tg1 of the resin composition contained in the insulating layer and a glass transition temperature Tg2 of the insulating base material included in each of the circuit substrates satisfy a relationship Tg1>Tg2.