To provide a technique capable of attaining high speed switching over a wide wavelength range with high switching efficiency.

The polarization direction of an optical signal is controlled by a polarization controller 11 so as to be orthogonal to a main axis of a polarizer 15. A control pulse generator 12 generates control pulses from a control beam with a wavelength which is different from the wavelength of the optical signal. The optical signal and the control pulse are inputted to a nonlinear optical fiber 14. In the nonlinear optical fiber 14, the optical signal, during a time period in which the optical signal and the control pulse coincide, is amplified with optical parametric amplification around a polarization direction of the control pulse. The optical signal, during the time period in which the optical signal and the control pulse coincide, passes through the polarizer 15.