。
He has guts.
Literal
He [topic-は] belly [subject-が] settled.
腹が据わっている ('the belly is settled') is an idiom meaning 'to have guts, to be unflappable.' Japanese idioms frequently locate courage and resolve in the belly (腹/肚) rather than the heart — 腹を決める ('set the belly' = decide), 腹が立つ ('belly rises' = anger), 腹を割る ('split the belly' = speak frankly). Short and idiomatic.