An apparatus 1 for mounting an annular tread ring R on an outer peripheral surface TS of a tire base T, which includes a tire base holding section 2 which is movable between a first position P1 and a second position P2 while holding the tire base T, and a tread ring mounting section 3 for mounting the tread ring R on the outer peripheral surface TS of the tire base T. The tread ring mounting section 3 comprises a tread holder 10 for holding the inner circumferential surface of the tread ring R, and a tread pushing-out device 11 for pushing out the tread ring R in the axis direction. At the second position P2, after placing the tread ring R on the outer peripheral surface TS of the tire base T in the tire base holding section 2, the tread ring mounting section 3 pushes out the tread ring R from the tread holder 10 toward the first position P1 by the tread pushing-out device 11. And the tire base holding section 2 moves toward the first position P1 at the same speed as the pushing-out speed of the tread pushing-out device 11. Thereby, the tread ring R is mounted on the outer peripheral surface TS of the tire base T.