Disclosed is a brace bar attached to an inner surface of a sound board of a guitar to prevent the sound board from being distorted, which has a modified shape to improve the flexibility of the sound board while maintaining the strength of the sound board, thus improving the resonance of the sound board and reducing a weight of the sound board. The brace bar includes a narrow portion having a cross-section with a profile of which at least one side extends vertically upward to a position of a predetermined height, thus forming a lower base part, and is bent inward at the position toward a center of the brace bar, and, thereafter, extends upward while being inclined at a predetermined inclination angle to form a tapered upper part.