An expansion guiding apparatus of an airbag includes a connector connected to the airbag and to a pillar trim. When the airbag expands, it pulls the connector, which folds the pillar trim. The connector may include direction-change pins and a wire extending from the airbag to the direction-change pins to the pillar trim, sequentially, and attached to the airbag and the pillar trim. The wire may include a hook with a notch, attaching the wire to the pillar trim. Alternatively, the connector may include a rotating bar, rotatable about a hinge on the inner panel, and a wire extending from the airbag to the rotating bar to the pillar trim, sequentially, and attached to the airbag and the pillar trim. The wire may include a hook with a notch, attaching the wire to the rotating bar. The pillar trim may include a hinge, a notch, or a soft material part.