A readily stretchable/contractible and locatable cantilever support includes a fixed seat, a first link body, a second link body, a bridge seat, a third link body, a fourth link body, a movable seat, a first length telescopic adjustment device and a second length telescopic adjustment device. One end of the first link body is pivotally connected with the fixed seat. One end of the second link body is pivotally connected with the fixed seat in adjacency to the first link body. The other end of the first link body is pivotally connected with the bridge seat. The other end of the second link body is pivotally connected with the bridge seat. One end of the third link body is pivotally connected with the bridge seat. One end of the fourth link body is pivotally connected with the bridge seat in adjacency to the third link body. The other end of the third link body is pivotally connected with the movable seat. The other end of the fourth link body is pivotally connected with the movable seat. The first and second link bodies are connected with the fixed seat and the bridge seat to form a quadrangular body. The third and fourth link bodies are connected with the bridge seat and the movable seat to form another quadrangular body. Two ends of the first length telescopic adjustment device are respectively pivotally connected with the first link body and the fixed seat. Two ends of the second length telescopic adjustment device are respectively pivotally connected with the third link body and the bridge seat.