advertising company; ad agency
A company that plans, creates, and places advertisements for clients.
He works for a major advertising company.
The company commissioned a new advertising agency.
She works at a major advertising company.
I started an advertising company with a friend.
広告会社 and 広告代理店 are often used interchangeably for an ad agency, but 広告代理店 stresses the agency's role of representing media outlets on behalf of advertisers.
company; firm; office · (Shinto) shrine · regional Chinese earth god; village built for such a god · counter for companies, shrines, etc. · incorporated body; corporation
Compound of 広告 (advertisement) + 会社 (company).