This experiment was performed to make clear the influences of surface roughness on surfaceheat transfer systematically. In giving roughness to a plate surface, we created artificial roughness by carving projections of a fixed pitch. And by changing the pitch and height of projection, we researched the influence of surface roughness. Main results are as follows : - A turbulent boundary layer which is influenced by surface roughness is formed at larger Reynolds' number than a certain Reynolds' number and in this region the results almost satisfy the following relation. Nu=K'·Re Where, Nu is Nusselt's number. The value of K' becomes maximam in every kinds of the height of roughness at h/p=0.055, which means the best heat transfer in such condition. The maximam value of K' becomes larger as the height of surface roughness becomes heigher.