The transverse motion of a saw-wire affects the cutting surface geometry in wire-saw slicing. To evaluate the magnitude of the wire transverse motion under no-slurry and no-workpiece conditions, which should be minimized before starting the slicing process, a high accuracy, noncontact device has been developed. The measuring head of the device is composed of a laser diode module and a dual-element photodiode between which a saw-wire is placed for measurement. This paper elucidates the appropriate positional configurations of the photosensitive surface of the dual-element photodiode and the laser beam focal point with respect to the diameter wire in the laser beam direction. Furthermore, a measurement experiment is carried out on a wire-saw machine under no-slurry and no-workpiece conditions. The paper reports and discusses the critical issues, such as measurement sensitivity, linearity, and accuracy.