PURPOSE:To improve space resolution, by differentiating the light receiving areas of a photoelectric transducing part, compensating the difference between light receiving sensitivities for three primary color light beams, and obtaining the optical currents having the values corresponding to the component ratio of the three primary color light beams in the light to be detected. CONSTITUTION:The light receiving areas of the light receiving elements 7r, 7b, and 7g of the light discriminating element 5' are different to each other. The light receiving area Sb of the light receiving element 7b for a blue color is set to be sufficiently larger than the light receiving areas Sg and Sr of the other elements 7g and 7r, and the area Sg is set to be larger than the Sr. Therefore the ratio of the areas Sb, Sg, and Sr are set so that the ratio is inversely proportional to the light receiving sensitivities to the three primary color light beams. The ratio of the optical current Ib, Ig, and Ir flowing the elements 7b, 7g, and 7r approximately corresponds to the ratio of the components of the three primary color light beams in the light to be detected.