The invention relates to an apparatus for host-based network separation, comprising: a network separation switch which, when a process is being executed on a host computer, checks whether the network allocated to the process is an internal network or an external network in accordance with the network access authority allocated to the process, and separates the process by IPs allocated to each network; and a packet processor which blocks the access of packet data when the packet data of the process separated by IPs by the network separation switch access a network other than the network to which the relevant IP is allocated.