A vehicle seat sliding apparatus includes: a first rail fixed to one of a vehicle floor and a seat and having first vertical wall portions, a first connection wall portion, and flanges; and a second rail fixed to the other one of the vehicle floor and the seat and having second vertical wall portions, a second connection wall portion, outward extending wall portions, and extending wall portions, wherein locking claws are aligned side by side at tip ends of the flanges of the first rail; the second rail is provided with through-holes; the vehicle seat sliding apparatus further includes, a locking member having locking portions, and a biasing member; and the outward extending wall portions are provided with flat portions.