PURPOSE: To present the intrusion of a noise into a magnetic recording signal and to improve the reliability of a magnetic disk device by attaching a socket (for a motor) for the rotation control signal. of a spindle motor through which larger current than a weak magnetic recording signal for a magnetic head, flows on the outside of a magnetic disk casing.

CONSTITUTION: The socket 7 inputting/outputting the magnetic recording signal (b) of the magnetic head 3 and a position control signal (c) of a positioning mechanism 4, the socket 8 inputting/outputting the rotation control signal (a) of the spindle motor 2 to the outside and the socket 9 inputting/outputting signals for the socket 7 and the socket 8 to an electronic circuit board 6 are attached to the inside of a magnetic disk casing 5 through connectors 10, respectively. The rotation control signal (a) flows from the spindle motor 2 to the socket 9 through the socket 8 and the connector 10, and the magnetic recording signal (b) flows from the magnetic head 3 to the socket 9 through the socket 7 and the connector 10. Further, the control signal (c) flows from the positioning mechanism 4 to the socket 9 through the socket 7 and the connector 10.