Provided are a tire manufacturing device and a tire manufacturing method capable of efficiently manufacturing a good-quality tire, wherein when the diameter of an annular tread is increased, the diameter of the tread is increased uniformly in a circumferential direction, and when the tread is mounted to a base tire, the tread is prevented from being mounted to the base tire while being displaced therefrom in a width direction. Specifically disclosed is a tire manufacturing device provided with a drum to which a base tire is affixed, a plurality of holding means each having a holding surface for holding the outer peripheral surface of an annular tread, a moving means for moving the holding means along the central axis of the base tire, a sealing means for sealing one opening of the annular tread, and an air supplying means for supplying air into a space surrounded by the annular tread and the sealing means, and the annular tread is mounted to the outer peripheral surface of the base tire.