To provide a shock absorbing device with a relatively short length for giving effective shock absorbing operation to any vehicle different in weight and speed.

The shock absorbing device 100 comprises a speed detector 2 for detecting a vehicle speed V, a weight detector 3 for detecting a vehicle weight M, a fluid bag 1 for generating shock absorbing force F on collision of a vehicle 300, a setter 5 for setting the shock absorbing force F of the fluid bag 1, and a processor 4 for inputting a speed signal and a weight signal from the speed detector 2 and the weight detector 3, respectively, computing the shock absorbing force F to be generated by the fluid bag 1 in accordance with the speed V and the weight M of the vehicle 300 and controlling the setter 5 in accordance with the computation result. The shock absorbing force F is established corresponding to the vehicle speed V and the vehicle weight M.