A control section according to an embodiment of the present invention is configured to: set, as a first temperature, a temperature obtained from a thermal image at a first position contained in a first infrared image corresponding to a surrounding environment in the thermal image, and set, as a second temperature, a temperature obtained from the thermal image at a second position contained in a second infrared image corresponding to a duct or the like in the thermal image; calculate an upper limit and a lower limit of a temperature range by using the first temperature and the second temperature; and control a display section to display the thermal image such that temperature distribution on the subject is represented by colors within the temperature range having the upper limit and the lower limit that have been calculated.