Abstract: The termite detecting device is placed in an expected invading passage for detecting damage or destruction caused by termites. One configuration of the device includes: a detecting wood sample for attracting termites; a detecting terminal being pressed against the detecting wood sample while the detecting wood sample is supplied with water as required; and a magnetic circuit capable of being opened and closed by the movement of the detecting terminal. When the detecting wood sample is eaten and damaged by termites and becomes fragile, the detecting terminal sinks into the detecting wood sample by virtue of a pressing force and the magnetic circuit is made open. As a result, the device detects the existence of termites. Alternatively, another configuration of the termite detecting device detects vibrations caused by termites so as to detect the invasion of termites.