An optical waveguide device and an optical communication module are provided. In the optical waveguide device which includes a core and a cladding layer formed around the core and has one end formed to be inclined so as to refract input and output signals, the core includes therein a diffraction portion for diffracting an optical signal incident through the cladding layer to propagate straight through the core. Thus, it is possible to prevent deterioration of an optical signal coupling ratio in implementing a technique of transmitting optical signals in opposite directions.