issuer; publisher
Refers to a person or organization that issues or publishes something, such as documents, certificates, securities, or publications.
The issuer of this certificate is the city office.
The publisher of that book is a major publishing company.
出版社 specifically refers to a publishing company, while 発行者 can be any issuer, including of certificates or securities.
Compound of 発行 (issue, publish) and 者 (person).