noun
substation; branch office
Typically refers to a local branch of a government office, such as a police substation or tax office branch.
交番は警察署の支署のようなものです。
A police box is like a substation of a police station.
税務支署で確定申告の相談ができます。
You can get advice on your tax return at the local tax office branch.
Compound of 支 (branch, support) and 署 (government office). The reading ししょ is the on'yomi of both characters.