| 摘要 |
A cartridge has at least two detection holes. When both the detection holes are opened, a pushing element inside a hole-detecting unit is retained at a highest position by the biasing force of a biasing element so as to be remote from a detecting switch by a predetermined distance. Thus, the switch is off, and a disc is write-protected. When either of the detection holes is closed, respective projections of the pushing element are pushed by the closed detection holes such that the pushing element comes into contact with the detecting switch. Thus, the switch is turned on, and the disc is writable.
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