A certificate can be used as a digital signature in a target document converted into an electronic file. A person who cannot perform the digital signature mandates the digital signature so as to allow a legal representative who is granted the delegated authority in law such as a real estate registration task or the like to carry out the digital signature using the certificate. A method for issuing a certificate for digital signature and a certificate issuance server receive a reference number and an authorized code from a terminal, generates a certificate the reference number and the authorized code, and output the generated certificate to the terminal. A method for mandating a digital signature and an electronic registration server receive a request of a digital signature for at least one target document from a terminal, and provide information of the at least one target document to the terminal, and thus the digital signature for the at least one target document that is provided to the terminal can be carried out.(510) Issue power of attorney for a digital signature(520) Issue a certificate(530) Perform a digital signature(AA) Start(BB) EndCOPYRIGHT KIPO 2016