A vehicle seat slide device includes: a first rail provided to extend in a front-rear direction of a vehicle and including first side wall portions, and first flanges overhanging from tips of the first side wall portions to inside and further folded to a base end side of the first side wall portions; a second rail joined to the first rail to be capable of moving in the front-rear direction and including second side wall portions, a connecting wall portion connecting base ends of the second side wall portions, and second flanges overhanging to an outside and further folded so as to be surrounded by the first side wall portions and the first flanges; and a locking member joined to the second rail to rotate around an axial line extending in the width direction and capable of restricting relative movement of the first and second rails.