Patent ID: 6847709

Claim:
A private branch exchange apparatus, capable of connecting a plurality of extensions to extension terminals and connecting at least one outside line, comprising: a timer which measures a present time; detecting means for detecting a re-setting of time in the timer and generating a detection signal; first storing means for storing a difference integration value corresponding to an amount of change from a reference value in response to the detection signal; second storing means for storing information necessary for an accounting calculation process for a call charge based on time information measured by the timer in association with a call-sending extension for each extension; and controlling means for making the second storing means store start time information supplied from the timer and the difference integration value supplied from the first storing means, in the second storing means in association with the call-sending extension, when the call has started, and making the second storing means store end time information supplied from the timer and the difference integration value, in the second storing means in association with the extension, when the call has ended.