It is commonly known that autonomic modulations are caused by depression, fatal arrhythmia, and vascular disease. This may lead to be an urgent need of a reliable physiological technology to evaluate autonomic modulations. The specific purpose of the current study is to examine the possibility of whether the Acceleration Plethysmography (APG) system can become a new useful tool to measure autonomic modulations. We verified the heart rate variability (HRV) analysis by APG whether it can be used as same as by the ECG. The HRV is interpreted from the a-a interval (Taa) on APG waves. We assembled the simultaneous measurement system of APG and ECG, examined the identities of the R-R interval (TRR) of ECG and the Taa of APG in six subjects of 22-60 old, and then compared variables in frequency domains of HRV by both APG and ECG. The results showed a close correspondence of the Taa and the TRR. Furthermore, when the regression formula was set as Taa=C^*TRR, the coefficient of regression (C) was 1.0002, 1.0001, 0.9997, 1.0000, 0.9999, 1.0001 respectively; whereas for each subject, the coefficient of determination was 0.9901, 0.9892, 0.9968, 0.9740, 0.9676, 0.9677 respectively (p<0.01) . As for the difference between APG and ECG, the coefficient of variation of HRV was merely 0.1-0.2%, and the LF/HF ratio as 0.1-0.4. If we carefully interpret the results of the frequency analysis, the APG system can be a useful objective methodology to evaluate autonomic modulations. Because of its simplicity in usage, it is expected to be employed in the occupational health or primary care.