Provided is a carbon fiber bundle for use in producing a fiber-reinforced resin having high mechanical characteristics. Specifically provided is a carbon fiber bundle which is a carbon fiber that is composed of carbon single fibers and that has a strand strength of 5900 MPa or more, a strand elastic modulus of 250 to 380GPa as determined by the ASTM method, and a knot tenacity of 900N/mm2 or more. Each carbon single fiber has not any surface uneven structure which extends on the surface of the single fiber in the lengthwise direction thereof and which has a length of 0.6[mu]m or longer, but has an uneven structure wherein the height difference (Rp-v) between the highest point (peak) and the lowest point (valley) on the surface of the single fiber is 5 to 25nm with the average roughness (Ra) being 2 to 6nm. The cross section of the single fiber has a length/breadth ratio of 1.00 to 1.01, and the mass of the single fiber per unit length is 0.030 to 0.042mg/m.