PURPOSE: To fully protect a crew by making the effective restraining limit of a seat belt a reclining angle correspondent to the slide adjustment position of a seat in the seat equipped with an informing means which detects the effective restraining limit so as to inform the result of the detection of the crew.

CONSTITUTION: The side face of a seat 1 is provided with a detecting means 2 which detects that the seat 1 is beyond an effective restraining limit in adjustment by means of a seat belt 15, so as to inform the result of the detection of a crew by a informing means 3. The detecting means 2 consists of a rotating member 2b which is freely rotated to the directions indicated by arrow heads B2 and C2 separately from the rotation of a seat back 1b, a switch 10 composed of 2 conductive elastic members 10a and 10b which are mutually projected in parallel out of the member 2b so as to be fixed, a wire 9 fixed at the end section of a rail 8 which rotates the rotating member 2b in proportion to the sliding distance and direction of the seat 1, and of a projected pin 7 which is projected out of the side face of the seat back 1b in the vicinity of the switch 10.