Iruka (イルカ)) is the stage name for Kanbe Toshie (神部としえ) born in Nakano, Tokyo in 1950.
The height of her career ran from ~1970 to ~2000, although she still occasionally releases new music today. (In May, 2014, she released an insipid song all in English sponsored by the International Union for the Conservation of Nature, which you can see / hear here.)
There is an excellent brief bio here.
[Note that there is also an anime character named Iruka]