比較N1
〜ならいざ知らず
if it's... that's another matter (but...) / ...is one thing, but...
Structure
N/普通形 + ならいざ知らず
Explanation
If it's A that's another matter, but the B case is different; used when the second case cannot be allowed.
Examples
社員ならいざ知らず、外部の人間に口出しされたくない。
Employees are one thing, but I don't want outsiders butting in.
子供ならいざ知らず、大人がそんなことをしてはいけない。
A child is one thing, but an adult shouldn't do that.
Note
Synonymous with ならともかく/はともかく, used when the second case cannot be allowed.