In a controller of a tape drive, when a command processing unit receives a Write FM0 command, a channel input/output unit writes the data in the buffer and a speculative FM onto the tape, and a CM input/output unit records speculative FM presence information in a cartridge memory. When the command processing unit receives Write FM1 command next, the CM input/output unit erases the speculative FM presence information from the cartridge memory. When the command processing unit receives a command other than Write FM1 command next, the channel input/output unit overwrites a speculative FM.