According to one embodiment, a spin-torque oscillator includes a non-magnetic unit, one or more first magnetic unit, and a second magnetic unit. The non-magnetic unit is formed of a non-magnetic body. The one or more first magnetic unit is connected to the non-magnetic unit and generates a pure spin current indicating the flow of the electron spin that does not accompany an electric charge current. The second magnetic unit is connected to the non-magnetic unit in a manner such that a distance between the second magnetic unit and the first magnetic unit is shorter than a spin diffusion length indicating a distance that an electronic spin polarization is maintained in the non-magnetic unit. The second magnetic unit oscillates by the pure spin current.