乐 is read lè 'joy' here, as in 乐园 'paradise', not yuè 'music'. Milton is also written 弥尔顿.
culture
The same title translates 渡边淳一's novel 失楽園 (Shitsurakuen), a 1997 bestseller about a love affair that ends in a double suicide; in Japan its title became a buzzword for an affair.