A magnetoresistive effect device including a magnetoresistive effect element with which a high-frequency filter can be realized is provided. Magnetoresistive effect device includes: at least one magnetoresistive effect element including a magnetization fixed layer, spacer layer, and magnetization free layer in which magnetization direction is changeable; first and second port; signal line; and direct-current input terminal. First and second ports are connected to each other via signal line. Magnetoresistive effect element is connected to signal line and is to be connected to ground in parallel to second port. Direct-current input terminal is connected to signal line. A closed circuit including magnetoresistive effect element, signal line, ground, and direct-current input terminal is to be formed.