To surely regulate the position of a roller in a seat slide device, eliminate risk causing a diagonal tumble during operation, smoothly perform turning of the roller, simplify a constitution, reduce a cost, facilitate assembly work and improve economical efficiency.

A roller 9a is mounted in a guide member 11 so as to hold an orthogonal condition relating to a lengthwise direction of a lower rail 2. The guide member 11 is formed by a guide groove 13 fitting the roller 9a, lower rail abutting surface formed in a lower part and an upper rail abutting surface formed in both side parts. the upper rail abutting surface is guided by both side parts 5b of an upper rail 5.