An electric acoustic stringed musical instrument is a combination between an acoustic stringed musical instrument and an electric system; while a player is bowing on the strings, the strings not only laterally vibrate but also are repeatedly elongated and shrunk so as to give rise to rolling motion and pitching motion of the bridge; a strain sensor sensitive to the lateral component force of the vibrations and another strain sensor sensitive to the longitudinal component force are provided in and on the bridge for producing electric signals; since the timbre of tones is varied dependent on the ratio between the lateral component force and the longitudinal component force, the player can express his artistic expression in the electric tones by strongly or gently pressing the bow onto the strings.