PURPOSE: To increase the reliability of operation against side collision by providing a means of transmitting compressive load due to collision at the side and/or door of a vehicle, and mounting a sensor on a frame connected to a vehicle body and inside a seat so as to operate the sensor upon receiving deformation to the side and/or door of the vehicle body.

CONSTITUTION: The side tube 12a of a frame protrudes edge members 18, 19 from the side face of a seat through a connecting member 12c. The edge member 18 is made to face the side surface of a door through a sheet panel 20 normally. A sensor 16 is disposed inside of the edge of the side tube 12a and mounted on a frame so as to be operated on the displacement of the edge part 18. The sensor is operated on compression load, transmits frame to a gas generator 14 through a fuse at a high speed to inflate a bag 15. It is thus possible to provide a system effectively and with high reliability against side collision.