To provide a power monitoring system, capable of suppressing power consumption for displaying data related to power consumption in a home and obtaining the most recent data related to power consumption with a desired timing.

A power measurement unit 19 measures power used in a home as time series power data; power data measured by the power measuring unit 19 are stored in a storage section 21 in time series; and an arithmetic processing section 22 calculates the data, related to power consumption for enlightening power saving, based on time series power data stored in the storage section 21 for displaying at a display section 24. Then, a control unit 23 stops the arithmetic processing operation of the arithmetic processing section 22, when the control unit is off, and executes arithmetic processing operation for calculating the data related to power consumption at the arithmetic processing section 22, only when the control unit is turned on.