We had previously measured the total drag of truncated pyramids whose surfaces had been shaped in wavy forms. The results had shown a reduction of total drag when compared with that in the case of a truncated pyramid with smooth surfaces, although all the truncated pyramids had had the same projected area to the main flow direction. We carried out direct numerical simulation for turbulent flow around a truncated pyramid to elucidate the mechanism of the total drag reduction. We used an immersed boundary method to express the two-dimensional truncated pyramid. The height of the truncated pyramid was 45.9 wall units, while the flow depth was 360 wall units. In the case of the truncated pyramid with smooth surfaces, it was found from the computational results that the mean velocity increased in the range near the uphill face of the truncated pyramid. The values of turbulence intensities and Reynolds shear stress were high in this region. The mean velocity decreased in the range near the downhill face of the truncated pyramid. These regions were consistent with the regions where vortices had appeared intermittently in the previous experiments.