Disclosed are a pneumatic tire and a tire cavity resonance suppression device in which noise by cavity resonance is effectively reduced without any changes in tire and rim production facilities. The pneumatic tire is constituted by that an object, which is changed in sectional area in accordance with a position in a tire circumferential direction, is fixed to a tread inner surface by a ring-shaped jig made of an elastic body. The tire cavity resonance suppression device includes an object changed in sectional area in accordance with a position in a tire circumferential direction and a ring-shaped jig made of an elastic body for locking the object to a tread inner surface of the tire.