In a magnetic nanowire, a magnetic domain wall (DW) can move along the wire when an applied magnetic field or a spin-polarized current is applied. A magnetic spin-valve device composed of two nanowires connected by a nanosized constriction was prepared, on which the presence of a pinned DW by nanoconstriction was detected by giant magnetoresistance effect. When the magnetic wire has a nanoconstriction, the DW configuration and width were largely affected by the shape of nanoconstriction. An asymmetric magnetotransport behavior observed in the experiments was interpreted by a micromagnetic modeling study.