An illuminance acquiring device calculates the intensity of light sensed by the image pickup device acquired every different exposure time, and acquires the calculated intensity of light. The illuminance acquiring device including a noise-model data calculating section calculating noise-model data for modeling an influence of a noise generated in the image pickup device by using image pickup data obtained by means of the image pickup at different exposure time; and an illuminance calculating section calculating the output value of the image pickup device in consideration of the influence of the noise from the noise-model data and the output value of the image pickup device, acquiring the light energy by using the calculated output value, and calculating the intensity of the sensed light.