A helical groove 1B is formed in the sliding surface 1A of a sliding bearing 1 over the entire axial region thereof. To establish the height of a peak 1a defined by the helical groove 1B, an imaginary reference line L extending parallel to the axis is formed which is determined such that the total cross-sectional area of all the peaks 1a is equal to the total cross-sectional area of all the valleys 1b when the helical groove 1B is considered in axial section. A height, as measured from the reference line L to the top 1a' of the peak 1a is chosen in the range of from 1 to 8 .mu.m. The space created by forming the valleys 1b allows the supply of lubricant oil to be increased, thereby simultaneously achieving a reduction in the frictional resistance and the occurrence of an impact sound.