An authentication device includes a first login module and a second login module. Upon a login request accompanied by entry of correct authentication information on any one of accounts, the first login module approves a request for first login using the account in account information, the account information comprising the registered accounts distinguished between one or more first accounts and one or more second accounts, the second accounts being allowed for proxy login using the first accounts. Upon a further request for login using any one of the first accounts in a login session started by the first login using any one of the second accounts, the second login module approves a request for second login using the first account, the first account having a preset proxy for approving the proxy login using the second account in the account information.