According to Official Guinness Records,
The longest series of published travel guides is the 'Rurubu' series which, as at 2 November 2010, consisted of 3791 editions. Rurubu has been published continuously by JTB Publishing (Japan) since August 1984.
Rurubu began modestly, publishing four editions in 1984. It expanded rapidly and was publishing more than 100 titles a year by 1993.
For a complete list of 2010 records, please visit 2010 Guinness Records in Japan.