In this paper we confirm the relation between the phases and phase errors of the beat signal at the lock-in region of the amplitude modulation type ring laser gyroscope by numerical calculation. Based on this facts, we, numerically, study the envelopes and magnitudes of the dither noise for statistically summing out the beat signal phase error, and we, experimently, confirm these numerical results. As a result, we find that the dither noise requires the increase gradient and the decrease gradient of the dither amplitudes, and those gradients should be combined with white noise. The magnitude of the dither noise which is satisfied with these requirements should be more than 5 percents of the average dither amplitude.