Fukuoka subway is divided in 3 lines:
* Kuko Line (Airport Line)
* Hakozaki Line
* Nanakuma Line
The Kuko Line and the Hakozaki Line joined in the Nakasu Kawabata station.
The Kuko Line is what we can call the main subway line of Fukuoka.
Here is the link of the Fukuoka City Subway website: