A multi-articulated link knee joint capable of detecting a bending angle of a knee section without causing problems of an installation space and wiring of a sensor is provided. A four-link knee joint includes a knee section of a four-link mechanism, a fluid cylinder that restrains an action of the knee section, a position detecting device that detects a position of a piston rod with respect to a cylinder tube as an extension and contraction amount of the cylinder, and a computer that acquires a bending angle of the knee section by converting the position detected by the position detecting device.
