To provide a moving device, not increasing the preload and causing no looseness by automatically eliminating a clearance between a contact body and a support rail even if the contact body and the support rail wear away.

A preload device 8 includes: a rod 10 abutted on the contact body 7 directly or through a transmitting member on one end side and provided on the support rail 2 to be moved in the direction of pressing the contact body 7; a first energizing member 20 energizing the rod 10 in the pressing direction; a casing 12 provided to cover at least a part of the outer peripheral surface of the rod 10 and formed to increase the distance between the inner surface 12a and the outer peripheral surface of the rod 10 as it goes in the pressing direction; and a spherical member 22 disposed in contact with the inner surface 12a of the casing 12 and the outer peripheral surface of the rod 10 in the casing 12.