By theoretical simulations we investigated the transport properties of oligoporphyrin molecular wires on assumption of the molecular bridge structures. It was found that the tape-porphyrin wires, where the macrocycles are linked by three C-C bonds aligned in parallel, show the metallic I-V curves, while the other conjugated porphyrin show the semiconducting I-V curves. These differences are found to originate from the differences of their HOMO-LUMO energy gaps. Next we studied the transport properties of the T-shape porphyrin wires where extra macrocycles are fused to the edge of the linear-shape tape-porphyrin molecules. The existence of the current loop is predicted in the vicinity of a metal cation site, which induces the magnetic field on top of it. It was also found that this magnetic field is useful in controlling locally the spin orientation of the metal atom, and has a detectable strength in an experiment. Finally we discussed the applicability of the current-induced magnetic field in the molecular devices such as unimolecular memories.