A vehicle seat slide device includes: an upper rail including a bracket support having side walls and an upper wall connecting upper ends of the side walls; a lower rail supporting the upper rail so as to be relatively movable; and a bracket fixed to the bracket support. A cutout portion open upward is formed in the bracket support, a nut member which can be screwed to a bolt inserted into the bracket support via a terminal of the bracket support is disposed in the cutout portion, the bracket includes first and second vertical walls having an insertion hole into which the bolt is inserted, and which oppose each other, the first vertical wall is fixed to the terminal, and the second vertical wall is arranged inside the cutout portion at a position where the nut member is interposed between the first and second vertical walls.