Double modular redundancy (DMR) is to execute an operation twice and detect a soft error by comparing the duplicated operation results. The soft error is corrected by re-executing necessary operations. The re-execution requires error-free input data and registers are needed to store such necessary error-free data. In this paper, a method to minimize the required number of registers is proposed where an appropriate subgraph partitioning of operation nodes are searched. In addition, using the proposed register minimization method, a minimization of the area of functional units and registers required to implement the DMR design is proposed.