A welding portion inspection device configured to inspect a welding condition of a welding portion formed when a plurality of works are welded together, the welding portion inspection device comprising: an irradiation portion (1, 5) configured to irradiate welding laser beam along a welding trajectory set in works plural times or irradiate inspection laser beam plural times along a scanning trajectory set in a molten pool of the work melted by the welding laser beam so as to weld together the works; a light receiving portion configured to receive return light including reflected light from the molten pool in the work by the welding laser beam or the inspection laser beam irradiated by the irradiation portion (1, 5), evaporation luminescence which is generated by evaporating of the work and thermal radiation light radiated from the molten pool in the work; and characterised by the following features: an extracting portion configured to extract a first component containing evaporation luminescence and a second component containing thermal radiation light from return light received by the light receiving portion; and an inspecting portion configured to inspect the welding condition of the welding portion of the work based on a ratio between intensities of the first component and the second component which are extracted by the extracting portion wherein the inspecting portion is configured to inspect the welding condition of the welding portion of the work by conducting Fourier transform on a ratio between the intensity of the first component and the intensity of the second component or a power of the ratio between the intensity of the first component and the intensity of the second component. an irradiation portion (1, 5) configured to irradiate welding laser beam along a welding trajectory set in works plural times or irradiate inspection laser beam plural times along a scanning trajectory set in a molten pool of the work melted by the welding laser beam so as to weld together the works; a light receiving portion configured to receive return light including reflected light from the molten pool in the work by the welding laser beam or the inspection laser beam irradiated by the irradiation portion (1, 5), evaporation luminescence which is generated by evaporating of the work and thermal radiation light radiated from the molten pool in the work; and characterised by the following features: an extracting portion configured to extract a first component containing evaporation luminescence and a second component containing thermal radiation light from return light received by the light receiving portion; and an inspecting portion configured to inspect the welding condition of the welding portion of the work based on a ratio between intensities of the first component and the second component which are extracted by the extracting portion wherein the inspecting portion is configured to inspect the welding condition of the welding portion of the work by conducting Fourier transform on a ratio between the intensity of the first component and the intensity of the second component or a power of the ratio between the intensity of the first component and the intensity of the second component. an extracting portion configured to extract a first component containing evaporation luminescence and a second component containing thermal radiation light from return light received by the light receiving portion; and an inspecting portion configured to inspect the welding condition of the welding portion of the work based on a ratio between intensities of the first component and the second component which are extracted by the extracting portion wherein the inspecting portion is configured to inspect the welding condition of the welding portion of the work by conducting Fourier transform on a ratio between the intensity of the first component and the intensity of the second component or a power of the ratio between the intensity of the first component and the intensity of the second component.