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 and a transmitting unit having a wireless communication function to transmit, by wireless, a sensor monitoring output, the sensor and wireless transmitting unit are activated intermittently, and, when the monitoring terminal device is not operating, supply of power to the sensor unit and transmitting unit is stopped and a control processor is put into a sleep state, which enables reduction of power consumption to a minimum. This ensures a long operation of the monitoring terminal device even in an environment in which power is not supplied from the outside.