We propose a novel background-field removal method to recover a local field of a brain edge. The proposed method consists of two steps. First, the background field of the brain edge is calculated from the total field by using local polynomial approximation. Second, the local field of the whole brain is calculated by regularization that enables sophisticated harmonic artifacts reduction for phase data (RESHARP) processing with the constraint term of the background field of the brain edge. The results from a human brain experiment showed that the method is useful for calculating the local field and susceptibility maps of the whole brain.