A noncontact optical system that can measure displacement or vibration of an object is designed by employing the oblique ray method. By using a single convex lens which serves as both the input and output lenses, we made the optical system very compact and reliable. In addition, the bandwidth of the vibration measurement is more than 100 KHz by using the position-sensitive detector as the beam position sensor. The resolution and capture range of the system are $pm$1 ${mu}{ extrm}{m}$ and 1100 ${mu}{ extrm}{m}$, respectively. As a sample test, the vibrations of a speaker and a rotating compact disc surface were measured.