A program downloading method downloads a program from a host unit to a plurality of network apparatuses. The program downloading method includes sending a configuration file comprising a main configuration file and a plurality of configuration files from the host unit to the plurality of network apparatuses, acquiring in each network apparatus a sub configuration file corresponding to a system type thereof from a main configuration file of the received configuration file, making from each network apparatus a send request requesting the host unit to send a load module name and a version required therein, based on a sub configuration file corresponding to the system type thereof, and storing in a standby memory of each network apparatus a load module which is received from the host unit in response to the send request.