Each agent unit gets status information indicating the state of each of network printers connected by a LAN from the network printers every first time period. Whenever each agent unit gets the status information from the network printer, it overwrites a status log data file with the gotten status information. Each agent unit converts all status information stored in the status log data file into status mail of electronic mail and transmits the status mail to a mail server every second time period longer than the first time period. On the other hand, a console unit accesses the mail server and reads the status mail in a proper time period to the console unit.