A method of manufacturing a circuit substrate including forming, in an insulating substrate and circuit patterns that are provided on a first surface and a second surface of the insulating substrate, a through-hole penetrating the insulating substrate and the circuit patterns, where the circuit patterns contain Cu as a main component. The method including filling, in the through-hole, an electrically conductive paste that is a melting-point shift electrically conductive paste including Sn—Bi solder powder, Cu powder, and resin, and forming a protrusion obtained by causing the electrically conductive paste to protrude from the through-hole. The method further including performing pressure treatment on the protrusion near the through-hole; and performing heat treatment on the insulating substrate whose protrusion is subjected to the pressure treatment and causing the circuit patterns and the electrically conductive paste to be electrically connected with each other.