Provided is an optical signal processing device that can operate simultaneously for a plurality of wavelength bands. The optical signal processing device includes a WDM coupler array including a plurality of WDM couplers for separating the C band and the L band for the respective ports; input/output port groups provided for the C band and the L band, respectively; a micro lens array; a diffraction grating; a lens; and a spatial light modulator arranged in this order. The spatial light modulator collects light at different positions for the respective wavelengths, thus allowing all wavelengths to be independently subjected to a phase modulation. Light subjected to the desired phase modulation by the spatial light modulator is reflected and is deflected to have an angle corresponding to any desired port of the input/output port group, and then is optically-coupled to an input/output port depending on the deflection angle.