The invention provides an apparatus for optically writing a data onto a non-exposed film being coated with photosensive material while moving the film to a predetermined direction. The data represents a film frame No., photosensitive emulsion lot No. and so on. The apparatus has two groups of LEDs being arranged with a pitch in parallel two lines being crossing at right angles to a film proceeding direction. The disposing position of LEDs on the one line differs by half of the pitch from that on another line. Therefore, the center of light spot on the one of spotted parallel line irradiated on the film does not face with that on another spotted line along the film proceeding direction. Further, the emission timings of the two groups of light emission sources are respectively controlled to have some time lag therebetween, thereby superposing partially the parallel two spotted lines.