A tire mounting device which comprises: a bead guide for pushing an inner circumferential end of a bead of a tire radially outwardly of a wheel while the bead guide circles about a center axis of the wheel under a state in which the tire is temporarily engaged on the wheel, and a roller for pressing the bead of the tire from above the tire while the roller circles about the center axis of the wheel to follow the bead guide; wherein the bead guide includes: a columnar portion having a cylindrical side surface; and a plate-like guide plate extending from a distal end of the columnar portion radially outwardly of the columnar portion, and wherein the bead guide is arranged at a position at which a bottom surface of the bead guide is opposed to an outer-circumferential-side upper surface of the wheel with an interval secured between the bottom surface and the outer-circumferential-side upper surface of the wheel; characterized in that the tire mounting device further comprises bead guide rotary position switching means (41, 90) for selectively switching, by rotating the bead guide, the bead guide between a first position at which the guide plate is retreated from an outer circumferential end of the wheel radially inwardly of the wheel, and a second position at which at least a part of the guide plate protrudes from the outer circumferential end of the wheel radially outwardly of the wheel, and the bead guide is switched from the first position to the second position so that the guide plate is caused to enter below the bead of the tire. a bead guide for pushing an inner circumferential end of a bead of a tire radially outwardly of a wheel while the bead guide circles about a center axis of the wheel under a state in which the tire is temporarily engaged on the wheel, and a roller for pressing the bead of the tire from above the tire while the roller circles about the center axis of the wheel to follow the bead guide; wherein the bead guide includes: a columnar portion having a cylindrical side surface; and a plate-like guide plate extending from a distal end of the columnar portion radially outwardly of the columnar portion, and a columnar portion having a cylindrical side surface; and a plate-like guide plate extending from a distal end of the columnar portion radially outwardly of the columnar portion, and wherein the bead guide is arranged at a position at which a bottom surface of the bead guide is opposed to an outer-circumferential-side upper surface of the wheel with an interval secured between the bottom surface and the outer-circumferential-side upper surface of the wheel; characterized in that the tire mounting device further comprises bead guide rotary position switching means (41, 90) for selectively switching, by rotating the bead guide, the bead guide between a first position at which the guide plate is retreated from an outer circumferential end of the wheel radially inwardly of the wheel, and a second position at which at least a part of the guide plate protrudes from the outer circumferential end of the wheel radially outwardly of the wheel, and the bead guide is switched from the first position to the second position so that the guide plate is caused to enter below the bead of the tire.