A seat slide device for a vehicle includes a first rail, which includes a first horizontal wall, a first vertical wall, and a first flange, and a second rail, which includes a second vertical wall and a second flange. A joining was connects the second vertical wall with the second flange. The coupling portion between the first horizontal and vertical walls includes a first ball guide. The basal end portion of the second flange includes a second ball guide. A first ball is arranged between the first and second ball guides. A restricting member that projects on the first horizontal wall functions to reduce a vertical space between the joining wall and the first horizontal wall and is contactable to the joining wall when the second vertical wall is deformed due to a load that is applied to produce pushing force between the first ball and the second rail.