Seat vibration when a vehicle is idling or in motion is an issue in automobile development. In order to reduce this vibration, dynamic damper or inertia mass is widely used. These countermeasures increases vehicle's weight and causes bad fuel-efficiency. Some new ways to reduce the vibration without weight increase are needed. One of that is the floating seat. Seat vibration has been reduced by controlling seat resonance frequencies. In order to control resonance frequency, the structures of the seat-mounting unit are replaced with floating structures using rubber bushings. It was demonstrated that partially replacing the mounting unit with floating structures makes it possible to control the resonance frequencies of the entire seat. The issue of balancing vibration reduction with strength and durability and crash safety performance caused by the fitting of rubber bushings to the seat-mounting unit was addressed using stopper structures optimized for each type of input. To adopt the floating seat in an actual vehicle, floating structures and a conventional foot bracket are combined. This combined foot bracket not only makes it easy to assemble floating structures into the seat, but also make it possible to keep the seat weight almost the same as a conventional seat. By using this floating seat, the vehicle gets same seat vibration performance as a conventional vehicle that has a dynamic damper in its seat. Thus, it is proved that the floating seat is a one of the lighter methods to reduce vibration than a conventional method using dynamic dampers or inertia masses.