PROBLEM TO BE SOLVED: To provide a knee joint that can prevent a collision of a leg portion against a stair when the leg portion is swung, while maintaining bending lock function and knee stretching function when the leg portion is stood up, and improving accuracy of positioning the leg portion when being swung.SOLUTION: A knee joint 1 includes: a lower leg-side member 3 having a base 31, a vertically-moving part 32 provided so as to be vertically movable with respect to the base 31, and an energizing means 33 that energized in a direction of lifting the vertically moving part 32 with respect to the base 31 when the vertically-moving part 32 is lowered from a reference position in the state where a floor reaction force is not applied to the vertically-moving part 32 a thigh-side member 2 having a thigh-side link part 21 which is rotatable with respect to the vertically-moving part 32 so as to be in a state of being bent at a predetermined angle with respect to a lifting direction of the vertically-moving part 32 at the reference position and a rotating means 4 that rotates the thigh-side link part 21 in a stretching direction as the floor reaction force increases and the vertically-moving part 32 lowers, and rotated the thigh-side link part 21 in a bending direction as the floor reaction force decreases and the vertically-moving part 32 is lifted up.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2016,JPO&INPIT
