In a power slide device for vehicle seat which moves an upper rail in the forward/rearward direction by rotationally driving a screw rod, by providing a screw rod supporting rail with a pair of load transmitting members that are spaced from each other in the forward/rearward direction and providing the screw rod with a load receiving member which is in contact with the pair of load transmitting members, bucking is supported at a plurality of points when the buckling occurs in the screw rod due to an axial force acting on the screw rod, and this limits the direction of the buckling to reduce the amount of the buckling.