A subordinate office of a company or organization, distinct from the head office (本社).
当社の大阪支社は梅田にあります。
Our company's Osaka branch office is in Umeda.
支社長に昇進した。
I was promoted to branch manager.
The company set up a branch office in Osaka.
Starting next month, I'm being transferred to the Nagoya branch office.
The head office oversees the branch offices across the country.
He works at the Tokyo branch office.