To allow a thermal spraying repair area and its surrounding area to be observed sharply, without being affected by flashlight of a spraying reaction during thermal spraying repair work.

An observation device 1 for a thermal spraying repair area is for illuminating and observing a damaged part 16 of a furnace wall 15 where a thermal spraying material 11 is sprayed to repair by thermal spraying, and includes an illumination part 4 and a filter 5. The illumination part 4 irradiates the damaged part 16 with illuminating light 8 in a wavelength band other than the wavelength band of the flashlight having combustion light emission of the thermal spraying material 11 and spontaneous light emission of the furnace wall 15 combined therein, and illuminates a furnace wall surface area 15a including at least the damaged part 16. The filter 5 shuts off flashlight of the thermal spraying reaction, and allows the illuminating light 8 reflected from the furnace wall surface area 15a to pass therethrough.