Magnetic disk device

A magnetic disk device comprising:

• a magnetic circuit including a lower yoke and an upper yoke, the upper yoke having a washer part formed in an outer area of the upper yoke and driving an actuator carrying a magnetic head, so that the magnetic head is moved to a target track on a surface of a magnetic disk;
• a base mounting a spindle motor which rotates the magnetic disk and having a threaded-hole part opposing the washer part;
• a screw being inserted to the washer part and the threaded-hole part and fastening the upper yoke to the base;
• and
• a blocking member arranged between the washer part and the threaded-hole part, the blocking member enclosing a gap outside the lower yoke between a bottom surface of the washer part and a top surface of the threaded-hole part,
• wherein the threaded-hole part is internally arranged in a column formation projection from a bottom plate of the base, and an inside surface of the blocking member is fitted in contact with an outside surface of the column formation of the base.