A spindle bracket of a torsion beam axle suspension system is defined on an end portion of a trailing arm to be connected to a hub assembly on which a wheel and a tire are mounted. The spindle bracket may include a first inner bracket that is welded to an inner side and an outer side of an end portion of a upper member of the trailing arm, a second inner bracket that is welded to an inner side and an outer side of an end portion of a lower member of the trailing arm, and an outer bracket that is attached to the first and second inner brackets to be engaged with the hub assembly in company with the first and second inner brackets.