A parking assist system that performs parking assist when a host vehicle is reversed to be parked in a perpendicular manner in a target parking space, the parking assist system comprising an electronic control unit configured to: when the host vehicle is reversed to be parked in the perpendicular manner in the target parking space, estimate first extending directions that are extending directions of obstacles respectively located on right and left sides of the target parking space in a state where the host vehicle moves across in front of the target parking space; calculate a planned moving path along which the host vehicle is reversed to be parked in the perpendicular manner in the target parking space, based on the estimated first extending directions of the obstacles respectively located on the right and left sides of the target parking space; as the host vehicle is guided into the target parking space while the host vehicle is reversed, estimate second extending directions that are extending directions of the obstacles respectively located on the right and left sides of the target parking space while updating the second extending directions until the host vehicle reaches a parking target position; determine whether the estimated and updated second extending directions of the obstacles respectively located on the right and left sides of the target parking space satisfy a predetermined condition; and when the updated second extending directions satisfy the predetermined condition based on a determination result, update the planned moving path by using the updated second extending directions instead of the first extending directions or the second extending directions before being updated, determine whether the host vehicle has reached the parking target position based on a predetermined criterion; and characterized in that the electronic control unit is further configured to: when at least one of the updated second extending directions satisfies the predetermined condition, determine whether the host vehicle has reached the parking target position by using a reach determination condition that is looser than a reach determination condition used in a case where neither of the updated second extending directions satisfies the predetermined condition. when the host vehicle is reversed to be parked in the perpendicular manner in the target parking space, estimate first extending directions that are extending directions of obstacles respectively located on right and left sides of the target parking space in a state where the host vehicle moves across in front of the target parking space; calculate a planned moving path along which the host vehicle is reversed to be parked in the perpendicular manner in the target parking space, based on the estimated first extending directions of the obstacles respectively located on the right and left sides of the target parking space; as the host vehicle is guided into the target parking space while the host vehicle is reversed, estimate second extending directions that are extending directions of the obstacles respectively located on the right and left sides of the target parking space while updating the second extending directions until the host vehicle reaches a parking target position; determine whether the estimated and updated second extending directions of the obstacles respectively located on the right and left sides of the target parking space satisfy a predetermined condition; and when the updated second extending directions satisfy the predetermined condition based on a determination result, update the planned moving path by using the updated second extending directions instead of the first extending directions or the second extending directions before being updated,