A device for management is attached to a copier, and the device for management is connected to a host computer at a management center via a telephone line. In a database of the host computer are provided a field for calculating an MCBJ since resetting or in a predetermined period, and a field for calculating a total MCBJ of copiers of a same model. Based on comparison between results obtained in these two fields, a warning is issued. Moreover, an MCBJ of a copier in a predetermined period is retained in the database for three consecutive such periods, so that a trend of the MCBJ of the copier is traced. A rising tendency of the MCBJ is judged from a combination of two trend-indicating values, one comparing an MCBJ two periods before with a current MCBJ and the other comparing the MCBJ two periods before with an MCBJ one period before. If the rising tendency exceeds a predetermined factor, a warning is issued.