Provided is a circuit board which suppresses abnormal formation of plated layer inside a via, caused by core materials of glass fibers or the like projected from a side wall of the via and which helps to improve the connection reliability of the via. An insulating layer, which is formed of thermoset resin and embedded with glass fibers, is provided between a first wiring layer and a second wiring layer. The glass fibers projected into a via hole side from a side wall of the via hole in different positions are embedded into a via conductor in such a state that the glass fibers are jointed with each other.