In an antenna device, power is fed from a first port to a first radiation element, and power is fed from a second port to a second radiation element. A decoupling circuit connects the first radiation element and the second radiation element, and includes a bridge element connecting a first point between the first port and the first radiation element and a second point between the second port and the second radiation element to each other. A first reactance element is provided in series with the first radiation element between the first point and the first radiation element, and a second reactance element is provided in series with the second radiation element between the second point and the second radiation element. At least one of the first reactance element and the second reactance element is configured so as to be capable of changing the value of reactance.