A vehicular seat slide device includes a lower rail, an upper rail supporting a seat above, a lock lever supported by the upper rail and configured to restrict the relative movement of the upper rail by engaging with the lower rail, a spring attached to the upper rail and biasing in such a manner that the lock lever engages with the lower rail. The spring includes a locking portion inserted in a locking hole provided at an upper edge of the upper rail and opening to a side surface of the upper rail, the locking portion is insertable into the locking hole by elastically deforming the spring body towards an inner side relative to the locking hole, the locking portion is restricted from being detached from the locking hole by being locked at a peripheral edge of the locking hole due to recovery of the elastic deformation.