An objective is to provide a key management apparatus in a document security and editing system that controls and manages the usage rights of a document, allows a user with usage rights to read and edit freely according to user qualification, and manages the usage rights in compliance with document management rules established by an organization. The key management apparatus includes an encryption key memory 11 that stores an encrypted document identifier of an encrypted document and an encryption key of the encrypted document; a usage rights set memory 13b that stores the encrypted document identifier and usage rights; a user group determiner 18b that determines the usage rights of a user; a usage rights issuer 16 that receives a read request using the encrypted document identifier, refers to the encryption key memory and the usage rights set memory, and sends the usage rights and the encryption key of the encrypted document; and an encryption information issuer 17 that receives an edit request, refers to the encryption key memory and the usage rights set memory, instructs to generate an identifier of a document to be encrypted and a encryption key of the document to be encrypted, and sends the generated identifier and the generated encryption key.