An apparatus is provided for optically writing or reading information comprising a row of optical dot array chips each including a plurality of optical dot elements constantly arranged in the direction of the row. The respective array chips are driven by separate control circuits (IC) each incorporating a plurality of drive transistors (TR1-TR64) for driving the respective optical dot elements of a corresponding array chip. Each control circuit further incorporates a gate voltage setting circuit (27) which applies an adjustable gate voltage (VG) to the respective drive transistors (TR1-TR64). The gate voltage setting circuit (27) comprising a plurality of parallel voltage dividing resistors (R1-R7) which are selectively incorporated into said gate voltage setting circuit (27).