A turbulent flow in a square pipe is investigated through a direct calculation of the discretized Navier-Stokes equations based on the control volume method. The direct numerical calculation approach is essentially free from any turbulence model. However, it generally requires a huge computational time and memory size, and is possibly performed on a relatively coarse grid system. Therefore, evaluation of the solution for the coarse grid system is important in practical applications. The computational results in this study are compared with the other experiment and the large eddy simulation (LES) results. It has revealed that the present calculation predicts the characteristic feature of the turbulent flow even with the coarse grid system, and quantitative improvement of the solution is achieved nearly in proportion to the grid resolution squared.