Bearings having a small clearance during normal operation are selected. In some cases, bearings having a negative clearance when mounted are selected, to generate internal stress which enables achieving various effects. This so-called preload can be applied only to rolling bearings and not sliding ones. The performance of bearings is greatly affected by the applied preload. Application of a heavy preload to enhance the stiffness at the spindle undermines the high-speed rotation performance. In contrast, when a light preload is applied for high speed rotation, the stiffness is undermined. Therefore, a variable preload method is required. This study aims to develop a variable preload device using a linear actuator of the ball screw type, and to perform the performance evaluation of the developed device. Our studies verified that the proposed device worked satisfactorily.