Provided are a high-speed superluminescent diode, a method of manufacturing the same, and a wavelength-tunable external cavity laser including the same. The electric capstan includes an air pump, a motor, a reduction gear and a winching roller, and further includes an engagement-disengagement gear, wherein the input shaft of the air pump is connected to or separated from the output shaft of the motor by the engagement-disengagement gear. A transmission unit sets the delay time and the driving amplitude of the driving pulse to be supplied to a plurality of adjacent transducer elements selected by an element selection unit among the transducer elements arranged in an ultrasonic probe, on the basis of the transmission delay condition and the transmission amplitude condition. The invention also relates to a holding rail that can be used in said holding device. The locking member extends through the through hole, and includes an engaging portion disposed on the inner surface of the housing body, and a control portion exposed from the through hole.