Carbon fiber precursor fiber bundle, production method and production device therefor, and carbon fiber and production method therefor

A carbon fiber precursor fiber bundle, said carbon fiber precursor fiber bundle:

• having 1 m−1 or less of a degree of intermingle between a plurality of small tows based on the hook drop method with a 10 g weight;
• and
• consisting of substantially straight fibers without imparted crimp, a tow of which straight fibers has a moisture content of 2.0% by mass or more and 5% by mass or less when housed in a container;
• wherein:
• the carbon fiber precursor fiber bundle has a widthwise dividing capability to maintain a form of a single aggregate of tows when housed in a container, such that when taken out from the container and guided into a firing step, the carbon fiber precursor fiber bundle spontaneously divides widthwise in the firing step into the plurality of small tows only by a tension generated in the firing step,
• the aggregate of tows is formed by intermingling monofilaments between a widthwise end of a small tow and a widthwise end of an adjacent small tow by air flow,
• a number of the monofilaments in each of the plurality of small tows is from 50,000 to 150,000, and
• the straight fibers consist of acrylonitrile-based polymers.