The quality of gears is classified according to deviations measured by a gear measuring machine by ISO 1328-1, and recently a system to evaluate gear measuring machines is to be established with the requirements of high precision gears. The purpose of our research is to develop an ultrahigh precision gear measuring machine with small uncertainty of measured values and repeatability less than 1 micro meter. To reduce the transmission errors caused by the mechanism in conventional gear measuring machines, the experimental instrument consisting of two direct drive axes, linear axis and rotary axis, has been developed and its performance has been verified by authors. The mechanism, control and fundamental performance of the experimental instrument are described in this paper.