A monitoring terminal device is provided which is capable of reducing its power consumption to a minimum and of being fully operated even indoors by using a solar cell as a power source. In the monitoring terminal device including a sensor unit, the transmitting unit to transmit, by wireless, a sensor monitoring output, and a control unit which control the sensor unit and the transmitting unit, further including a power supply section, when only state change of object to be monitored, that is, a output of the sensor unit is detected the control unit and the transmitting unit are started to transmit monitoring information by the sensor unit. When the sensor unit and the generating section are not activated supply of power to the sensor unit and the generating section is stopped and the control unit by itself is put into standby state, which enables reduction of power consumption to a minimum. This ensures a operation of the monitoring terminal device even in an environment in which power is not supplied from the outside.