Results of analysis of a very simple, compact interferometer for recording holographic diffraction gratings, which allows continuous tuning of the angle between the interfering beams from 0° to 80°, are presented. The device consists of a single optical element, a beamsplitter cube. The lengths of arms in such an interferometer are automatically equal, and tuning is accomplished by changing the angle of incidence of the beam on the input face. Formulas for calculating the principal characteristics of the device are derived. It is shown that using a cube material with a higher index of refraction allows increasing the beam diameter and broadening the tuning range. Recommendations on the device design are provided.