Wavelength selective switch, and optical unit for wavelength selective switch

This wavelength selective switch is provided with: at least one input port (10a); a dispersion section (30), which wavelength-disperses light inputted from the input port (10a); a light collecting element (40), which collects the light that has been wavelength-dispersed by means of the dispersion section (30); a deflection section (50), which deflects the light that has been collected by means of the light collecting element (40); at least one output port (10b-10e), which outputs, as output light, the light that has been deflected by means of the deflection section (50); and an optical path correction section (20), which is disposed in the optical path between the input port (10a) and the dispersion section (30), and which shifts, with respect to the deflection section (50), the light incident positions of light to be wavelength-dispersed by means of the dispersion section (30).