PROBLEM TO BE SOLVED: To provide a monitoring device of a structure and its monitoring system capable of transmitting a measurement result simultaneously by radio without requiring a special power source.
SOLUTION: This monitoring device 3 is a device for monitoring the state of the structure such as a bridge, and is installed on a plurality of measuring points on the bridge. When a train passes on the bridge, the bridge is vibrated and the power corresponding to the vibration is generated from a piezoelectric material 4. The power generated from the piezoelectric material 4 is accumulated in a power accumulator 7, and the power is measured by a control part 8 and the measurement result is stored in a storage part 9. When a transmission command of the measurement result is received from a communication device separated from the monitoring device 3 by a radio communication part 10, the measurement result is read out of the storage part 9 by the control part 8 and the measurement result is transmitted by the radio communication part 10. In this case, since the measurement result is transmitted by the radio communication part 10 by using the power accumulated in the power accumulator 7 as a power source, the state of the bridge can be monitored with no power source and the measurement result can be transmitted wirelessly.