A wavelength selective switch for multiple units comprising: a plurality of input/output port groups (50-1, 60-1, 50-2, 60-2) including a plurality of input/output port arrays for transmitting a plurality of light beams each including a plurality of wavelength channels; a switching lens portion configured such that the plurality of light beams transmitted from the plurality of input/output port arrays intersect on a switching axis, wherein the switching lens portion is a cylindrical lens having a curve on the switching axis; a first prism portion arranged between the plurality of input/output port arrays and the switching lens portion, the first prism portion being configured to refract the plurality of light beams transmitted from the plurality of input/output port arrays at different angles on the switching axis according to different light beam groups, wherein the first prism portion includes a plurality of first incident surfaces; a second prism portion arranged after the switching lens portion, the second prism portion being configured to align a center line of each light beam group transmitted from the switching lens portion in parallel with an optical axis, wherein the second prism portion includes a plurality of second incident surfaces; a beam expansion portion configured for expanding a beam size of each light beam transmitted from the second prism portion in a direction of a dispersion axis, wherein the beam expansion portion includes a first beam expansion lens and a second beam expansion lens; a beam splitting portion configured for splitting each light beam whose beam size has been expanded by the beam expansion portion at different angles on the dispersion axis according to different wavelength components, wherein the beam splitting portion includes a prism part and a grating part; an imaging lens portion configured to readjust and focus the wavelengths of the light beams split by the beam splitting portion; and a switching portion including a plurality of divided areas corresponding to the plurality of input/output port groups (50-1, 60-1, 50-2, 60-2), the switching portion being configured to change an angle of a beam with a selected wavelength on the switching axis such that the wavelength selected from the plurality of wavelength channels of an input port which is selected independently from each group is transmitted to an output port of the plurality of input/output port groups (50-1, 60-1, 50-2, 60-2) which is selected independently, wherein the switching portion includes a plurality of switching channel portions configured to reflect the light beam output from the imaging lens portion according to the wavelengths. a plurality of input/output port groups (50-1, 60-1, 50-2, 60-2) including a plurality of input/output port arrays for transmitting a plurality of light beams each including a plurality of wavelength channels; a switching lens portion configured such that the plurality of light beams transmitted from the plurality of input/output port arrays intersect on a switching axis, wherein the switching lens portion is a cylindrical lens having a curve on the switching axis; a first prism portion arranged between the plurality of input/output port arrays and the switching lens portion, the first prism portion being configured to refract the plurality of light beams transmitted from the plurality of input/output port arrays at different angles on the switching axis according to different light beam groups, wherein the first prism portion includes a plurality of first incident surfaces; a second prism portion arranged after the switching lens portion, the second prism portion being configured to align a center line of each light beam group transmitted from the switching lens portion in parallel with an optical axis, wherein the second prism portion includes a plurality of second incident surfaces; a beam expansion portion configured for expanding a beam size of each light beam transmitted from the second prism portion in a direction of a dispersion axis, wherein the beam expansion portion includes a first beam expansion lens and a second beam expansion lens; a beam splitting portion configured for splitting each light beam whose beam size has been expanded by the beam expansion portion at different angles on the dispersion axis according to different wavelength components, wherein the beam splitting portion includes a prism part and a grating part; an imaging lens portion configured to readjust and focus the wavelengths of the light beams split by the beam splitting portion; and a switching portion including a plurality of divided areas corresponding to the plurality of input/output port groups (50-1, 60-1, 50-2, 60-2), the switching portion being configured to change an angle of a beam with a selected wavelength on the switching axis such that the wavelength selected from the plurality of wavelength channels of an input port which is selected independently from each group is transmitted to an output port of the plurality of input/output port groups (50-1, 60-1, 50-2, 60-2) which is selected independently, wherein the switching portion includes a plurality of switching channel portions configured to reflect the light beam output from the imaging lens portion according to the wavelengths.