To provide an optical transmitter element capable of significantly improving the accuracy and the volume of information obtainable from an optical transmitter element to achieve an accuracy of about 50 nm in standard deviation in 5000 lines per inch, and a positioning device using the same.

The invention provides an optical transmitter element equipped with a bar code for measuring a position or a length of a machine part by rotating or moving straightly and a positioning/length measuring device incorporated with the same. The optical transmitter element is characterized by using a three-dimensional structure configured so that the bar code is comprised of flat parts formed on a plurality of bit strings and between the bit strings and incident lights from the bar code are diffracted and interfered.