Visibility instrument

The utility model discloses a visibility meter, the power supply circuit of which comprises an external power supply circuit and an internal power supply circuit, wherein, a socket connector, a safety device and a lightning grounding device which are used for connecting the external power supply circuit are in series connected with each other in turn in the internal power supply circuit; a pressure-sensitive device is in series connected between the earth end of the lightning grounding device and the ground. Under the normal working condition, the pressure-sensitive device is in a high resistance state, so as to reduce common-mode voltage interference in the internal power supply circuit; once the visibility meter encounters lightning, the internal power supply circuit produces strong surge current and large surge voltage, and the pressure-sensitive device is started and conducted; when the voltage produced when the surge current contacts with the ground is larger than the threshold voltage of the pressure-se