is a Japanese light novel series written by Yasukiyo Kotobuki and illustrated by Johndee. It began serialization on the user-generated novel publishing website Shà Âsetsuka ni Narà  in February 2016. It was later acquired by Media Factory who began publishing it under their MF Books imprint in September 2016. A manga adaptation illustrated by 888 began serialization on Kadokawa's ComicWalker manga website in April 2018. A second manga adaptation illustrated by Maneki titled The Diary of a Middle-Aged Teacher's Carefree Life in Another World began serialization on Square Enix's Manga Up! manga website and app in October of the same year.
Written by Yasukiyo Kotobuki, The Diary of a Middle-Aged Sage's Carefree Life in Another World began serialization on the user-generated novel publishing website Shà Âsetsuka ni Narà  on February 7, 2016. It was later acquired by Media Factory who began releasing it with illustrations by Johndee under their MF Books light novel imprint on September 23, 2016. Twenty volumes have been released as of February 2025. The light novels are licensed in English by J-Novel Club.
A spin-off light novel series, titled Arafà  Kenja no Isekai Seikatsu Nikki Zero: Sword and Sorcery World, began publication under the same imprint on August 25, 2023.
A manga adaptation illustrated by 888 began serialization on Kadokawa's ComicWalker manga website on April 25, 2018. The manga's chapters have been collected by Media Factory into eight tankà Âbon volumes as of February 2025.
A second manga adaptation illustrated by Maneki, titled The Diary of a Middle-Aged Teacher's Carefree Life in Another World, began serialization on Square Enix's Manga Up! manga website and app on October 16 of the same year. The second manga's chapters have been collected into seventeen tankà Âbon volumes as of January 2026. The second manga is published digitally in North America by Square Enix via their Manga Up! Global app.
A manga adaptation of the spin-off series, illustrated by Piyoko Hatori, began serialization on Frontier Works's FW Comics Alter manga website on December 15, 2025.
By April 2022, the series has over 2.2 million copies in circulation.