To automatically distinguish a working condition of an apparatus so as to sum up a power amount by mutually distinguishing a standby condition and a working condition of the apparatus from a detected current and individually summing up and displaying an integrated standby power amount and an integrated working power amount.

This power monitor is provided with a power source connection unit 2 to an outlet connected to an alternating current power source 1, an apparatus connection unit 4 to an apparatus 3, and a current detecting means 6 detecting a current from a current transformer 5 detecting a current flowing through the apparatus 3. From a current found by a current carrying time counting means 7 detecting current carrying time to the apparatus 3 on the basis of an output from the detecting means 6 and by the detecting means 6, a quasi-power amount assuming a power source voltage as 100 V is found. From this value and the current carrying time, an integrated power amount consumed by the apparatus 3 is found by means of an integrated power amount computing means 8. From the output of a condition determining means 10 determining a working condition of the apparatus 3 from the output of the detecting means 6 and the output from the computing means 8, integrated power amounts are summed up individually so as to be indicated at a real time. In this way, a working condition of the apparatus can be gripped at a glance.