。
I'm an extremely honest man.
Literal
I [topic-は] this above-not honest man is.
この上なく ('without anything above this, supremely') is a literary intensifier — 'this is the maximum, with no upper limit.' 実直 is a formal na-adjective meaning 'honest, steady, straightforward.' 男 ('man') is being used as an identity noun. The combination feels slightly self-aggrandizing but earnest.