PURPOSE: To facilitate the attaching and detaching of a spindle body and improve the centering accuracy by surrounding the periphery of the spindle body with a front housing and a motor housing, and holding front and rear bearings in the respective housings.

CONSTITUTION: A built-in motor spindle device 1 is provided with a motor housing 3 held by a unit supporting member 2, a front housing 4 connected to the front of the motor housing, and a spindle body 5 inserted into the housings 3, 4. Then, a stator 6 such as a coil is shrink fitted into the intermediate, inner peripheral surface of the motor housing 3, and a rotor 7 such as a magnet is shrinkage fitted onto the intermediate outer peripheral surface of the spindle body 5. In this case, when this device is manufactured, the inner peripheral surfaces of both the housings are simultaneously machined with the housings 3, 4 connected to each other, front and rear bearings 12, 17 are fitted into the inner peripheral surfaces, and thus the spindle body 5 is rotatably borne by these bearings 12, 17.