Vibration tests on an intermediate heat exchanger (IHX) with a helically coiled tube bundle were performed by using a partial model to focus on investigating the complicated vibrational behavior induced by the interaction through the seismic stop between the center pipe and the bundle. The experimental results were compared with the calculated values obtained from a simple model in which the bundle was treated as a combined mass with the center pipe. As a result, it was confirmed that the simple model is useful in predicting the vibrational behavior of the IHX.