1. A solid-state imaging device comprising: an imaging device comprising an imaging area including a plurality of pixel blocks each of which includes a plurality of pixels; an image formation lens forming an image on an image formation plane by using light from a subject; an aperture unit including a plurality of aperture elements provided to associate with the plurality of pixel blocks, each of the aperture elements having aperture portions and shield portions, light from the image formation lens being filtered by each aperture element, at least one aperture element having an associated aperture portion that is disposed symmetrically about a center axis of the aperture unit with respect to an associated shield portion of the at least one aperture element, wherein the center axis is perpendicular or approximately perpendicular to an optical axis of the image formation lens; a microlens array including a plurality of microlenses provided to associate with the plurality of aperture elements in one-to-one correspondence, the plurality of microlenses being located so that a light passing through an aperture element passes through an associated microlens, each of the microlenses forming an image in the imaging area by using light filtered by an associated aperture element; and a signal processing circuit configured to process a signal of an image taken in the imaging area and estimates a distance to the subject.