A vehicle seat structure, comprising: a vehicle seat including a seat cushion configured to support the buttocks and thighs of an occupant; a movable member that is fixed to the vehicle seat and that moves in a seat front-rear direction together with the vehicle seat; a fixed member that is fixed to a floor of a vehicle body and that engages with the movable member and supports the movable member so as to allow movement of the movable member in the seat front-rear direction; and a lock mechanism configured to restrict movement of the movable member with respect to the fixed member, and also configured so as to permit movement of the movable member toward a seat front side with respect to the fixed member by at least part of the lock mechanism deforming when a force toward the seat front side, arising due to inertia, acts on the vehicle seat in conjunction with a collision in a state in which the movable member is engaged with a seat rear side portion of the fixed member; the lock mechanism including a plurality of engagement portions (52, 54) provided at the fixed member so as to be disposed at intervals along the seat front-rear direction, and including an engaging portion provided at the movable member and configured to engage with the respective engagement portions (52, 54); movement of the movable member in the seat front-rear direction with respect to the fixed member being permitted in a state in which the engaging portion is not engaged with the engagement portions (52, 54); movement of the movable member in the seat front-rear direction with respect to the fixed member being restricted in a state in which the engaging portion is engaged with the engagement portions (52, 54); and a strength of peripheral edge portions of a plurality of the engagement portions (52, 54) disposed toward the seat rear side being lower than a strength of peripheral edge portions of a plurality of the engagement portions (52, 54) disposed further toward the seat front side than the plurality of seat rear side engagement portions. a vehicle seat including a seat cushion configured to support the buttocks and thighs of an occupant; a movable member that is fixed to the vehicle seat and that moves in a seat front-rear direction together with the vehicle seat; a fixed member that is fixed to a floor of a vehicle body and that engages with the movable member and supports the movable member so as to allow movement of the movable member in the seat front-rear direction; and a lock mechanism configured to restrict movement of the movable member with respect to the fixed member, and also configured so as to permit movement of the movable member toward a seat front side with respect to the fixed member by at least part of the lock mechanism deforming when a force toward the seat front side, arising due to inertia, acts on the vehicle seat in conjunction with a collision in a state in which the movable member is engaged with a seat rear side portion of the fixed member; the lock mechanism including a plurality of engagement portions (52, 54) provided at the fixed member so as to be disposed at intervals along the seat front-rear direction, and including an engaging portion provided at the movable member and configured to engage with the respective engagement portions (52, 54); movement of the movable member in the seat front-rear direction with respect to the fixed member being permitted in a state in which the engaging portion is not engaged with the engagement portions (52, 54); movement of the movable member in the seat front-rear direction with respect to the fixed member being restricted in a state in which the engaging portion is engaged with the engagement portions (52, 54); and a strength of peripheral edge portions of a plurality of the engagement portions (52, 54) disposed toward the seat rear side being lower than a strength of peripheral edge portions of a plurality of the engagement portions (52, 54) disposed further toward the seat front side than the plurality of seat rear side engagement portions.