Provided is a power supply wiring structure which comprises a first and a second power supply wirings, which are disposed on different planes to cross each other two-dimensionally. The first and second power supply wirings are interlayer-connected by a first via at a crossing area where those power supply wirings cross each other. An extension wiring which is formed by partially extending from the crossing area along a wiring extending direction of other power supply wiring is provided at least to either the first power supply wiring or the second power supply wiring. The extension wiring and either the first power supply wiring or the second power supply wiring, which are disposed on a different plane from the extension wiring to face the extension wiring, are interlayer-connected by a second via. Thereby, generation of electro migration can be suppressed.