An artificial knee joint is provided whose rollback amount and roll ratio are small in slight flexion and large in deep flexion. In the artificial knee joint, a femoral component 20 includes a medial condyle 21, a lateral condyle 22, a first sliding surface 24 for coupling posterior ends of the medial condyle 21 and the lateral condyle 22, while leaving an opening 23 therebetween, and a second sliding surface 25 positioned above the first sliding surface 24. A tibial plate 30 includes a medial fossa 31, a lateral fossa 32, a post 36 protruding superiorly from between the media fossa 31 and the lateral fossa 32 to be inserted into the opening 23, a third sliding surface 34 with which the first sliding surface 24 is in contact at a posterior surface of the post 36, and a fourth sliding surface 35 with which the second sliding surface 25 is in contact behind the post 36. The first and fourth sliding surfaces 24 and 35 are convex curved surfaces. The fourth sliding surface 35 is posterior to the third sliding surface 34. The artificial knee joint takes a first sliding state in which the first sliding surface 24 is in contact with the third sliding surface 34, or a second sliding state in which the second sliding surface 25 is in contact with the fourth sliding surface 35, according to a flexion angle.
