To provide a multilayer wiring substrate in which a surface flatness is good and which is excellent in electric characteristic and conduction reliability.

In the multilayer wiring substrate, a resin insulating layer 4 and a wiring conductor layer 5 are alternately laminated on the wiring board 1 having a conductor layer 3 on a top surface. The multilayer wiring substrate connects the wiring conductor layer 5 and the conductor layer 3 electrically via a through-conductor 6 in the resin insulating layer 4 between the wiring conductor layer 5 located up and the conductor layer 3 located down. The wiring board 1 is constituted of an insulating substrate 2, a resin coating layer 10 having a through-hole and stuck directly on the substrate 2, and the conductor layer 3 provided so as to bury the through-hole. The conductor layer 3 is composed of a main conductor, and a ground conductor with the coefficient of thermal expansion smaller than the main conductor covering continuously the side face and the bottom.