The electronic band structure in the metallic copper is worked by the orthogonalized plane wave method in which the crystal potential is constructed by using both the Hartree's self-consistent field of Cu+ ion cores with exchange and conduction electrons with the Slater's approximate exchange potential. The approximate energy versus \veck curve is obtained, which shows the strong resemblance to the free electron behaviour along three directions in \veck space, i.e., (1.0.0), (1.1.1) and (1.1.0). The results of the various methods of approximations performed so far are compared with ours together with some critical discussions.