To provide a black panel thermometer for a weatherable light testing device capable of easily reading the graduation on a temperature display part.

This black panel thermometer having the temperature display part, wherein a display part illumination lamp having a contact mechanism and a display part illumination power source on a lighting circuit is disposed, has a means having a function for switching the contact mechanism between the ON/OFF states inside a window frame part of a weatherable light testing device body. The contact mechanism is switched to the ON state during a period when the black panel thermometer can be observed from a window part of the weatherable light testing device body by automatic rotation of a sample frame suspending the black panel thermometer, and the temperature display part is irradiated with light from the display part illumination lamp, to thereby facilitate reading of a displayed temperature.