A disk drive unit is provided that is capable of reasonably, smoothly opening/closing
a shutter by rotation of an inner rotor. The disk drive unit is configured such
that an inner rotor (4) is reasonably, smoothly rotated by sequentially
engaging a shutter opening/closing starting projection (72), a rack portion
(74), and a shutter opening/closing ending projection (76) of a rack
member (71) with a shutter opening/closing starting recess (26),
a partial gear (27), and a shutter opening/closing ending recess (28)
in the outer periphery of the inner rotor (4).
