An inspecting device for inspecting for a failure related to luminance unevenness in a light-emitting surface of a plane light source device of an edge-lit type, the failure being a brightness-darkness pattern appearing at an end of the light-emitting surface along a first edge thereof, the inspecting device comprising: an image acquiring unit which is configured to acquire a light-emitting surface image as a photographed image of the light-emitting surface of the plane light source device in a lit state; an inspecting unit which is configured to: - set an inspecting range, the inspecting range being an area of the light-emitting surface image corresponding to an area of the light-emitting surface at the end of the light-emitting surface and extending along the first edge; - generate, from the inspecting range of the light-emitting surface image, a one-dimensional luminance profile comprising a plurality of luminance values, each of the luminance values corresponding to one of the positions along the first edge in the inspecting range, - detect extreme values (P1-P15) in the luminance profile, the extreme values being local minimum values and local maximum values of the plurality of luminance values; - calculate an evaluation value for evaluating a difference between adjacent extreme values (P1-P15), and - determine that there is a failure if the evaluation value is larger than a predetermined threshold value; and an output unit which is configured to output information obtained by the inspecting unit, said information including at least a result of the determination of the presence or absence of the failure; wherein the inspecting unit is configured to calculate the evaluation value for an extreme value (P2-P14) of interest on the basis of the extreme value (P2-P14) of interest and two adjacent extreme values (P1-P15) by the following expression: HS = abs val 2 − val 1 + abs val 2 − val 3 val 1 + 2 × val 2 + val 3 where the extreme value (P2-P14) of interest is val2, and the two adjacent extreme values (P1-P15) are val1 and val3, and abs() is a function used to obtain an absolute value. an image acquiring unit which is configured to acquire a light-emitting surface image as a photographed image of the light-emitting surface of the plane light source device in a lit state; an inspecting unit which is configured to: - set an inspecting range, the inspecting range being an area of the light-emitting surface image corresponding to an area of the light-emitting surface at the end of the light-emitting surface and extending along the first edge; - generate, from the inspecting range of the light-emitting surface image, a one-dimensional luminance profile comprising a plurality of luminance values, each of the luminance values corresponding to one of the positions along the first edge in the inspecting range, - detect extreme values (P1-P15) in the luminance profile, the extreme values being local minimum values and local maximum values of the plurality of luminance values; - calculate an evaluation value for evaluating a difference between adjacent extreme values (P1-P15), and - determine that there is a failure if the evaluation value is larger than a predetermined threshold value; and - set an inspecting range, the inspecting range being an area of the light-emitting surface image corresponding to an area of the light-emitting surface at the end of the light-emitting surface and extending along the first edge; - generate, from the inspecting range of the light-emitting surface image, a one-dimensional luminance profile comprising a plurality of luminance values, each of the luminance values corresponding to one of the positions along the first edge in the inspecting range, - detect extreme values (P1-P15) in the luminance profile, the extreme values being local minimum values and local maximum values of the plurality of luminance values; - calculate an evaluation value for evaluating a difference between adjacent extreme values (P1-P15), and - determine that there is a failure if the evaluation value is larger than a predetermined threshold value; and an output unit which is configured to output information obtained by the inspecting unit, said information including at least a result of the determination of the presence or absence of the failure; wherein the inspecting unit is configured to calculate the evaluation value for an extreme value (P2-P14) of interest on the basis of the extreme value (P2-P14) of interest and two adjacent extreme values (P1-P15) by the following expression: HS = abs val 2 − val 1 + abs val 2 − val 3 val 1 + 2 × val 2 + val 3 where the extreme value (P2-P14) of interest is val2, and the two adjacent extreme values (P1-P15) are val1 and val3, and abs() is a function used to obtain an absolute value.