A middle-aged demon near 40 switches his career to become a Dungeon Master!? It was a "paradise" with no power harassment and no unpaid overtime...♪ —— I climbed my way up from a mere soldier to a general in the Demon King's army. But the order I received from the female Demon King was to be seconded to the "Dungeon Public Corporation," which handles the development and operation of dungeons in the demon world. Though I challenged this new frontier with no confidence, with the support of a beautiful secretary and a cute dungeon artisan, I succeeded in launching a dungeon that is hugely popular among human adventurers...!?