In the Littman type cavity, wavelength can be changed without mode hopping by rotating the tuning mirror. In the high resolution spectroscopy, the fine frequency scanning of approximately 30 GHz ($1 cm^{-1}$) is needed. The fine scanning is usually difficult in the Littman type cavity, and the wedge prism has been inserted into the Littman type cavity in this study. With this cavity, the single longitudinal mode was obtained. This was confirmed by measuring etalon fringe using a CCD camera and also by measuring linewidth simultaneously. For the frequency stability, wavelength was measured 10 times per 1 sec. using a wavemeter. As the wedge prism was rotated, frequency was measured by the wavemeter. By comparing the theoretically calculated grating mode and the longitudinal mode with the experimentally measured data, It was found that the frequency followed the grating mode, and the mode hopping occured when it came close to the nearest longitudinal mode. The frequency was changed by 62.5 GHz without mode hopping by rotating the wedge prism from $10.65^\circ$ to $13.74^\circ$. Theoretically, approximately 66 GHz frequency change was possible without mode hopping between $10.55^\circ$ and $13.75^\circ$ of the wedge prism angle. The measured results were in good agreement with the theoretical values.
