Needless to say, various rotational machines support today's industry. It follows that maintenance of these machines is extremely important to ensure their performance. Maintenance keeps facilities or machines able to operate, and can be defined as measures to restore a trouble or a fault. Maintenance is broadly divided into the two categories breakdown maintenance and preventive maintenance. In the case of breakdown maintenance, machines are fixed after the occurrence of troubles, so machines unpredictably stop operating. On the other hand, preventive maintenance is like car inspection; that machines are overhauled at intervals in according to a prescribed schedule. However, in breakdown maintenance it may be necessary to change parts which have not broken yet but are expected to break with time. Therefore, preventive maintenance is costly, but can result in cost saving. In contrast, recently a condition monitoring maintenance method has been adopted as preventive maintenance, in which inspection and repair are determined by monitoring machine condition. Such maintenance can allow machines to continue operation and save maintenance cost. ISO watching vibration as condition monitoring is widely applied to various rotational machines (motors, pumps, etc.). In this standard, we judge velocity of machine vibrations while the machine is driven according to a standard corresponding to the size of the machine. However, when the operational situation prevents rigid fixation of a machine to the ground, the machine is flexibly fixed. As a result, the machine vibration is higher amplitude than that of a machine that is rigidly fixed, and application of the existing evaluation standard becomes difficult. Therefore, the evaluation standard is relaxed for some machines. This study proposes new criterion that consider for stiffness and damping of a flexible support base that contains springs or rubber sheets. In this study we prepare an experimental system of one disk rotor that is supported by ball bearings at both ends, and compare vibration with a flexible support base and that with a rigid support base, by simulation and experiment.