An electric contrabass has a bridge structure on a body in which an inner space is defined, and the body is further formed with a slit under the bridge structure so that the lid of the body vibrates like a cantilever; a vibration sensor is provided inside the body, and has a vibration sensitive surface held in contact with the lower surface of the lid; while a player is bowing the strings, the vibrating strings excite the lid through the bridge structure, and the vibrations of the lid is converted to an electric signal through the vibration sensor; since the distance from the vibrating strings and the single vibration sensor is approximately equal, the single vibration sensor produces the electric signal without undesirable imbalance and interference.