To effectively protect an occupant from a shock at collision by arranging a folding type inflatable bag received in a case on a part apt to receive the shock of a motorcycle, and inflating and developing the inflatable bag when the shock of the motorcycle is detected by a collision sensor.

A folding type inflatable bag received in a case as a safety device is arranged on a part apt to receive the shock of a motorcycle such as the lower part of an operation board, the front part of a windshield screen, or the side part of a front flow regulating plate. A collision sensor detecting a shock of the motorcycle is arranged on the proper place of the front part of the motorcycle, and connected to a safety device. When the collision sensor detects collision, the inflatable bag is inflated and developed by jet of gas. The inflatable bag at developing can be provided with reinforce on the exposed side to the shock if necessary. Further it can be divided into 2-3 chambers so as to be continuously in order inflated.