A photoelectric conversion element includes a semiconductor layer including a pair of p.sup.+ regions in which p-type impurities are doped, and a p.sup.- region which is disposed between the p.sup.+ regions and has a lower p-type impurity concentration than the p.sup.+ regions. A gate electrode is formed over the p.sup.- region via a gate insulation film, thus, a p-MOS structure is formed. A width of the gate electrode is less than a width of the p.sup.- region. A p.sup.- region, which is a portion of the p.sup.- region and is located immediately below the gate electrode, forms a light receiving layer, and p.sup.- regions, which are portions of the p.sup.- region and are located away from below the gate electrode, form LDD regions. The photoelectric conversion element is fabricated on the same substrate as a thin-film transistor for a driving circuit, thereby constructing a display device with an input function.