expression
one of one's hobbies; a source of enjoyment
Colloquial expression used to describe something that brings personal pleasure or is a favorite pastime. Often used in the pattern ～が一楽だ or ～を一楽とする.
読書が一楽だ。
Reading is one of my hobbies.
彼は釣りを一楽としている。
He enjoys fishing as a hobby.