Judging from his appearance, he might be a soldier.
Literal
Appearance from judge-[if-ば], he [topic-は] soldier might-be-[かもしれない].
様子 ('appearance / look / manner') is the object of judgment. ~から判断すれば ('if one judges from X') is a fixed analytical phrase. かもしれない ('might be / possibly'). Distinct from にちがいない which expresses confident inference — かもしれない is hedged.