A network system includes a management apparatus and multiple apparatuses. The management apparatus includes a preparation instruction unit to transmit an instruction to prepare a certificate request to the apparatuses; a collection unit to collect the certificate requests; a request unit to request issuance of certificates to a certificate authority; a resetting instruction unit to transmit the issued certificates to the apparatuses and to instruct resetting of certificates. The apparatus includes a storing unit including an operation area for storing a first certificate and a provisional operation area; a provisionally operating unit to transfer the first certificate to the provisional operation area, and to generate a certificate request, and to transmit the certificate request to the management apparatus; a setting unit to store a second certificate, issued by the certificate authority, in the operation area, and to instruct a communication unit to conduct the communication by switching a certificate.