To simply constitute a seat structure for a vehicle capable of equipping it with a function to assist its pretensioner device or function to substitute the pretensioner device effectively using any existing structure effectively.

Mats 21-25 in the shape of thin sack are provided on the surface of the seat part 1 or backrest 2 of a seat, and there a seat belt 12 is arranged. When a pre-collision condition sensor 40 senses that the vehicle body is in the condition immediately before collision, fluid is supplied quickly to the mats 21-25.