A hybrid wind musical instrument is a combination of an alto saxophone and an electronic system, and a player has an option between acoustic tones and electronic tones to be produced during performance; the electronic system includes sensors monitoring selected component parts of the key mechanism so as to determine the electronic tones intended to be produced by the player, and plural combinations of pieces of magnet and Hall-effect elements serve as the sensors: However, the component parts of key mechanism are arranged in a narrow space over the surface of tubular instrument body; driven parts are attached to the selected component parts so as to bridge gap between the selected component parts and the Hall-effect elements remote from the selected component parts.