The actuating device is capable of automatically eliminating a clearance between a contact body and a rail. The actuating device comprises: a moving body guided by the rail; the contact body contacting the rail; and a pressure unit biasing the contact body toward the rail or in a pressing direction. The pressure unit comprises: a rod having one end, which contacts the moving body, and the other end, the rod being capable of moving in the pressing direction; a first biasing member biasing the rod; a casing covering an outer face of the rod, the casing having an inner face, whose distance from the outer face of the rod is gradually reduced toward the other end of the rod; and a spherical body contacting the inner face of the casing and the outer face of the rod.