A packet communication apparatus sends an authentication request packet received from a user terminal to an authentication server. If a packet received from the authentication server is an authentication packet for the user terminal, an authentication controller executes authentication processing of the authentication packet. If the authentication packet includes connection limit information for the user terminal, a connection limit controller sets the connection limit information to the user terminal. According to the connection limit information, the packet communication apparatus sends the packet received from the user terminal to a quarantine server disposed to quarantine the user terminal.