Abstract: A folding arm mounted on a column of a musical instrument stand has a seat mounted on the column. The seat has a ring. A tube is perpendicular to the column and extending outwards from the ring. A passage is longitudinally defined in the tube. A slot is longitudinally defined through a front end of the tube. An elbow has a rear part pivotally mounted in the slot by a pivot pin. Two movable pieces are received in the passage and pushed by the rear part to tightly abut the column when the elbow is perpendicular to the column. A bar is mounted on a front part of the elbow. Whereby, when the elbow is perpendicular to the column, the arm is secured on the column. When the elbow is pivoted to a position parallel to the column, the arm is movable for adjusting the support height of the stand.