PURPOSE: To improve the turning accuracy by making the height of a rotary head coincident with the center of gravity of the rotary part and a position where the radial load moment of two radial bearings is 0.

CONSTITUTION: The height of the magnetic recording and reproducing head, the center of gravity of the rotary part and a position where the radial load moment of radial bearings is 0 are made nearly coincident with each other. That is the center of gravity of the rotary body is adjusted to be coincident with the height of the head by adjusting the weight of a rotary body gravity center adjusting weight 17 mounted to a rotor case 15 and the rotary body gravity center position adjusting weight is calculated by calculation or peliminary experiment so that the moment of mass is zero at the height of head. Thus, weight is formed incorporatedly with other rotary member, e.g., the rotor case 15. That is, a part of the thickness of the rotor case 15 is increased corresponding to the calculated weight so as to attain incorporation.