We formulate a local gauge-invariant theory for the electromotive force induced by domain-wall dynamics in a ferromagnet. We demonstrate that this emf generation is a real-space topological pumping effect. The integral of the emf over one pumping period is a quantized topological invariant which does not depend on the details of the domain-wall configuration nor on its detailed dynamics. Based on our theory, the full instantaneous electric potential distribution can be mapped out by standard electrostatic methods. We also provide further details on our recent experiments which confirmed the emf induced by domain-wall dynamics.National Science Foundation (U.S.) (Grant No. DMR-0906025)National Science Foundation (U.S.) (Grant No. DMR-0903812)Robert A. Welch FoundationUnited States. Dept. of Energy. Division of Materials Sciences and EngineeringUnited States. Dept. of Energy (Grant No. DEFG03-02ER45958)