Two light receiving elements are formed on a support substrate. A first light receiving element is formed of a p-type layer, an n-type layer, a light absorption semiconductor layer, an anode electrode, a cathode electrode, a protection film, etc. A second light receiving element is formed of a p-type layer, an n-type layer, a transmissive film, an anode electrode, a cathode electrode, a protection film, etc. The light absorption semiconductor layer absorbs light in a wavelength range λ and disposed closer to the light receiving surface than is the pn junction region. The transmissive film has no light absorption range and disposed closer to the light receiving surface than is the pn junction region. The amount of light in the wavelength range λ is measured through computation using a detection signal from the first light receiving element and a detection signal from the second light receiving element.