PURPOSE: To provide seat installation structure capable of moderating various demands for precision on a car body side rail itself, its installation, installation of a seat on a seat side rail, etc., and improving workability and durability of a slide device.

CONSTITUTION: A support bracket 30 to install a seat with a bolt 60 is fastened on a seat side rail 22 assembled on a car body side rail 21 free to move longitudinally, a bolt receiving hole 33 is provided on the support bracket 30 and an elastic bush 40 to engage with the bolt 60 free to elastically deform and to grow a play of the seat against the seat side rail 22 is fit on the inner margin of the bolt receiving hole 33.