In order to give a formalism to calculate from the first principle the electronic structure of substitutionally disordered alloys in the coherent potential approximation (CPA), we reformulate the CPA based on the t-matrix of the muffin-tin potential and extend the KKR method of the energy band calculation to concentrated alloys by introducing the concept of the coherent t-matrix. In close connection with this, a formulation is given to calculate, with the use of the locator and coherent locator, the local and total densities of states of alloys based on the tight-binding model. In this model the transfer integral as well as the atomic level depends on the atomic species on sites, and the transfer integral between A and B atoms, TAB, is assumed to be a geometrical mean TAA and TBB. The effect of the dependence of the transfer integral on atomic species is discussed by numerical calculations.