A seat sliding device for preventing accidental operation of the operation member. The lock member 50 fixes (locks) the upper rail 20 fixed to a vehicle seat and the lower rail 30 fixed to the vehicle floor via the front and rear feet so as not to make a relative movement. The lock member 50, with the lock nails 55 of the pivoting member 50b, pivots around the pivot center L extending in the rail sliding direction, in response to the operation of the operation lever, and the pivot center L is positioned distant from the lock nails 55.