An optical system and an information apparatus using the optical system are provided. The optical system includes an optical bench on which a light source and a photodetector including a main photodetector receiving the light are mounted. A lens unit is coupled to the optical bench, and an optical path separating member separates an optical path of light emitted from the light source and propagating toward the lens unit and an optical path of light incident from the lens unit. The optical system may include a monitor photodetector and/or an optical path forming unit coupled to the optical bench. The monitor photodetector receives a portion of the light emitted from the light source. The optical path forming unit includes a first mirror reflecting the light emitted from the light source and a second mirror reflecting the light incident from the lens unit and reflected by the first mirror.