A technology for easily forming a multi-layer wiring structure that is fine and reliable. In the multi-layer wiring structure, the lower-layer wiring and the upper-layer wiring that are formed to sandwich an insulating layer are electrically connected to each other in a projection formed in the lower-layer wiring. The projection includes a columnar conductive member and the upper and lower layers thereof and each of the lower layer and the upper layer is formed of a conductive layer formed over the entire lower-layer wiring. The upper-layer is electrically connected to the lower-layer wiring in the portion where the projection is exposed substantially on the same plane as the top surface of the insulating layer.