Objective: The purpose of this study was to investigate the apparent mass of the sitting human body and to compare it with current experimental data and the ISO 5982 standard impedance model. Method: The apparent mass of the seated human body in the vertical direction was measured. Twelve male subjects were exposed to random whole-body vibration of frequency range (1-20 Hz), with a vibration excitation level of 1.0 m/s² r.m.s. The body posture was upright with no backrest contact. Results: The obtained apparent masses were compared to the International Standard, (ISO 5982). The biodynamic response of the seated Japanese subjects peaked in the 4-6.5 Hz frequency range, which is little bit higher than the reported range of fundamental frequencies (4.5-5 Hz) in most other studies which used different experimental conditions. The outcomes show a clear difference between apparent mass of Japanese subjects and ISO 5982 data. Conclusion: It is not sufficient to apply the ISO 5982 standard to Japanese vehicle design or dummy design.