1. An optical position sensor comprising: a light shading plate having a first slit and a second slit, as light introduction ports, defined therein, said first slit and said second slit intersecting each other; and a light reception portion including a first unidimensional light reception sensor and a second unidimensional light reception sensor, said first and second unidimensional light reception sensors being disposed so as to oppose said light shading plate with a predetermined gap therebetween, said first and second unidimensional light reception sensors including a plurality of photo-electric conversion devices, said first unidimensional light reception sensor being disposed so as to cross only said first slit and said second unidimensional light reception sensor being disposed so as to cross only said second slit.