A waveguide type grating device according to the invention includes a quartz substrate, a cladding and two waveguides. Waveguides are arranged to provide an input port, an Add port, an output port, a Drop port, directional 3 dB couplers, core width-changing portions, and grating portions each interposed between core width-changing portions. The width of core is changed between each non-grating portion and each grating portion in an adiabatic structure, for example, a parabolic structure. For this structure, a waveguide type grating device is structured to suppress the increase in wavelength loss due to coupling from progressive propagation mode to regressive radiation mode, with less cost and smaller dimension.