A measuring device measures sensitivity distribution of a photo sensor including a light projector element for projecting detection light externally, and a photoreceptor element for receiving the detection light reflected externally, and photoelectrically detects an article. The measuring device includes a test panel, having a test pattern, formed on a surface thereof and in at least two colors, for being read by the photo sensor photoelectrically for inspection. A moving mechanism moves the test panel relative to the photo sensor and at a regular speed. A controller actuates the moving mechanism, and evaluates an output from the photoreceptor element, in order to determine the sensitivity distribution of the photo sensor according thereto. Sensitivity distribution of the photo sensor is initially expressed two-dimensionally. Also, a plurality of the sensitivity distribution being obtained are used to determine sensitivity distribution of the photo sensor expressed three-dimensionally.