To provide a wiring substrate which has a capacitor built therein and can reduce capacitances and inductances between signal vias.

A wiring substrate 100 has first and second connection terminals 103 and 104 forming a dense area 112 on its major surface 101. A capacitor 20 including a power electrode layer 31, a grounding electrode layer 32 and high dielectric layer 76 is built in the interior of the substrate. Coaxial grounding via conductors 144 are provided around signal via conductors 145 passed through the high dielectric layer 76 to reduce capacitances and inductances between the signal via conductors 145 by its sealing effect.