The discloser provides a multi-input and multi-output optical switch capable of switching over all WDM wavelengths. An optical switch according to one embodiment includes: an optical demultiplexing element (3) that demultiplexes an optical signal from at least one input port into individual wavelengths; a first optical deflection element (5), which deflects an incident optical signal, that deflects the wavelength-separated optical signal incoming from the optical demultiplexing element to change a traveling direction for each wavelength to a switch axis direction perpendicular to a wavelength dispersion axis direction; a second optical deflection element (8) that deflects the optical signal incoming from the first optical deflection element to change the traveling direction to the switch axis direction for output to at least one of the output ports; and an optical multiplexing element (10) that multiplexes the optical signal with the different wavelengths incoming from the second optical deflection element.