To provide efficient and nimble performance by providing an inner cylinder interposed into the seat post of a frame so as to be free in moving vertically and having an up and down engage slit, and a saddle support rod operatable right and left through a spring in the middle thereof, and operating the brake of a handle through sliding of the tip thereof and a cylinder cam in the seat post.

In a shock absorber equipped with a spring 16 always acting upward on an inner cylinder 8 interposed into the seat post 2 of a bicycle frame 1 so as to be free in moving vertically and having an up and down engage slit 11, a saddle support bar tip 12 is engaged with a cylinder cam 14 on the inner cylinder 8, and the support bar tip 12 slides by the operation of a brake lever 5 of a handle so that the saddle support bar 12 moves down. At a riding time on the bicycle, when a handle lever is grasped, the brake lever and a descending device are interlocked by a wire division board, and when a hand or a waist touches the saddle, the saddle moves down so as to be easy to ride. In the case of stopping on riding or feeling any danger, the saddle moves down when the lever of the handle is grasped so that both feet can touch ground.