A tread pattern of a tire is disclosed which has wave-shaped and straight grooves capable of maintaining desired block rigidity and hydroplaning performance of the tire. In the tread pattern, which includes circumferential main grooves, transversal grooves formed between adjacent ones of the circumferential main grooves, and blocks formed between adjacent ones of the transversal grooves, at least one of the circumferential main grooves has a wave-shaped structure having opposite inclined side surfaces each comprising an upper surface portion having first and second curved surfaces alternately arranged along a circumferential direction of the tire while having substantially opposite curvatures, respectively, to form a continuous wave-shaped surface, and a lower surface portion having a straight side surface connected to the alternate first and second curved surfaces while extending along the circumferential direction to form a circumferential straight groove.