PURPOSE: To optionally vary a pre-load amount by constituting a pre-load load member by a piezoelectric element actuator and a support plate thereof, voltage- driving the piezoelectric element actuator so that a minute change is given in the axial direction.

CONSTITUTION: When a nut 4 is fastened to give a pre-load, a piezoelectric element actuator 9 is expanded and contracted in the axial direction. This expanded and contracted amount is changed by changing the magnitude of a voltage to be added. According to this constitution, the applied voltage is regulated to a minute amount to generate a minute expansion and contraction, whereby the pre-load is optionally regulated after a bearing is assembled into a device.