PURPOSE: To follow with high accuracy an aimed pattern set in such a way that a vibrational movement of an ultrasonic oscillator becomes at a const. angle speed if possible by controlling a mechanically-scanning type ultrasonic scanner with an ultrasonic oscillator and a sensor detecting a vibrational condition thereof.

CONSTITUTION: When a diagnosis mode is input, an aimed pattern θr of a movement angle for driving a motor is prepd. by a motor-driving pattern generating part 23. When a direct vibration is used, this aimed pattern θr coincides with a vibrational pattern of an ultrasonic oscillator 37 and various patterns can be easily formed by changing each a variable value. When an aimed movement of a motor 25 is determined, an input pattern θr2 into the 1st controlling part 27 on every trial is changed and renewed by the 2nd controlling part 31 constituted of a repeating control. If a rotational angle θ of the motor can not follow the aimed movement angle θr, to compensate this delayed part, an input θr2 into the 1st controlling part 27 is increased or decreased to coincides finally the rotational angle θ of the motor with the aimed movement angle θr. No fluctuation on speed is generated thereby and following with high accuracy can be performed.