To provide a breaker and a power monitoring system for measuring used power per branched breaker and presenting it to a user.

A current flowing through a power line 11 is measured by a power measuring section 12, and the power is measured on the basis of a current measured value. The measured value of the power measuring section 12 is transmitted by a radio communication section 13 to an information processing device. When the measured value is transmitted to the information processing device, an ID is added to measure based on the ID as to which branched breaker has transmitted the measured value. Power required for the operations of the power measuring section 12 and the radio communication section 13 is supplied from a battery 14. The battery 14 is charged with the power generated by a noncontact power feed device 15. The measured value received by the information processing device is processed, thereby obtaining the present power consumption per branched breaker. The obtained power consumption of each branched breaker is displayed to present the used power to the user.