A magnetoresistance effect device includes a first port, a second port, a magnetoresistance effect element, a first signal line that is connected to the first port and applies a high-frequency magnetic field to the magnetoresistance effect element, a second signal line that connects the second port to the magnetoresistance effect element, and a direct current application terminal that is connected to a power source configured to apply a direct current or a direct voltage in a lamination direction of the magnetoresistance effect element. The first signal line includes a plurality of high-frequency magnetic field application areas capable of applying a high-frequency magnetic field to the magnetoresistance effect element, and the plurality of high-frequency magnetic field application areas in the first signal line are disposed at positions at which high-frequency magnetic fields generated in the high-frequency magnetic field application areas reinforce each other in the magnetoresistance effect element.