In an apparatus, each of light receiving elements outputs an intensity signal based on a corresponding intensity of return light from a measurement space. The return light includes reflected light reflected based on reflection of the measurement light by a target object. An identifying unit identifies a light receiving area in the light detection region as a function of the intensity signals of the respective light receiving elements. The light receiving area is based on specified light receiving elements in the plurality of light receiving elements. The specified light receiving elements are arranged to receive the reflected light. A distance measuring unit measures the distance of the target object in accordance with the intensity signals received by the specified light receiving elements.