A network management apparatus inputs a plurality of work dates and time periods to update software in a base station. The apparatus obtains an n-week average of the numbers of connection calls during each of the input time periods for each day of the week, based on statistical information about connection with a wireless terminal in each base station. The apparatus obtains an m-month average of the numbers of connection calls during each of the input time periods for each date, based on the statistical information. The apparatus calculates, for each of the time periods for a work date, an average or a weighted average of the n-week average and the m-month average to obtain a degree of impact upon a communication service. A processing section selects a work date and a time period having the minimum degree of impact and updates the software.