PURPOSE: To protect magnetic tape data in a magnetic tape output device which does not check logical data such as a volume label by providing a magnetic tape device output means which executes the output processing of data corresponding to an output request to a magnetic tape when a recognition mark is not stored.

CONSTITUTION: When the magnetic tape device output means 17 receives an output processing request from an output processing program 16, it recognizes whether a write prohibition control mark is written in a magnetic tape medium or not through a write prohibition detection means 7. When the recognition mark is detected in a first storage area, a request invalidation notice means 8 gives a notice that the output request is invalid to the output processing program 16. When the recognition mark is not recognized, a data block is written into the data block area of a magnetic tape medium 11 in a magnetic tape device 10. Thus, magnetic tape data can be protected in the output device which does not check logical data such as the volume label.