<p>It is well known that the power of low-frequency and high-frequency components of heart rate variability decreases in individuals with diabetes who have diabetic autonomic neuropathy, based on the frequency domain analysis of 24-h electrocardiograph recording. In the present paper, we examined the frequency and power of sinusoidal components within the low-frequency and high-frequency bands using generalized harmonic analysis applied to the R–R interval time series from both individuals with diabetes and healthy controls. In the control group, there were significant differences in frequencies between the first and other components in the low-frequency band. On the other hand, in the individuals with diabetes, there were no significant differences in the component frequencies. In both groups, there were no significant differences in the component frequencies in the high-frequency band. Our present results suggest that diabetes mellitus narrows the frequency band range of the low-frequency component in heart rate variability. This result might help elucidate the mechanism underlying how low-frequency power decreases in individuals with diabetes. Thus, in the spectral analysis of heart rate variability, the use of generalized harmonic analysis enables power calculation differently from traditional methods. We anticipate further diffusion and accumulation of evidence concerning the evaluation of heart rate variability indices using generalized harmonic analysis.</p>