This paper presents a new method of measuring of small inclination angles. The method consists in application of a pendulum with a diaphragm coworking with an optoelectronical barrier. Results of studies of the constructed device are also presented, they focused on determination of drift of the measured inclination angles as well as variation of the period of the complete oscillation of the pendulum for positive and negative angles of inclination. Variation of mean errors of the studied magnitudes for all test measuring series were analyzed graphically.