A Public Key Infrastructure (PKI) using a certificate has already been widely used in a variety of fields for the provision of security service Accordingly a Certification Authority (CA) that issues a certificate must securely construct a Certification Authority System and manage it It is significantly important for a CA to ensure its service to continue to operate properly by preparing for any disaster caused by a CA's private key compromise no matter what the cause is. In this paper, we provide the definitions of PKI disaster recovery and PKI business continuity, which are more clear and specific than ever before We also present three requirements for a PKI model preparing for a disaster Then we propose a PKI model that ensures business continuity in the event of a disaster in which a CA key is exposed It is easily applied to the existing PKI structure We stress that the proposed PKI model in this paper is the first to ensure both applicability to the existing models and business continuity in the event of a disaster.