A woodwind instrument has a key mechanism for selectively closing and opening tone hole chimneys formed on a tube, and the key mechanism includes keys supported by a linkage at the associated tone hole chimneys; each of the keys includes a retainer inserted between a pad cup and a pad, and the retainer has a backing plate portion held in area contact with at the inner surface thereof to the pad and in point contact with at the outer surface thereof to the pad cup so that an assembling worker adjusts the pad to an appropriate attitude in the pad cup by pressing the pad to the associated tone hole chimney, and, thereafter, secures the retainer to the pad cup; this results in that the player can seal the tone hole chimney with the pad through a simple adjusting work.