A waveguide device includes: an electrically conductive member having an electrically conductive surface; a waveguide member having an electrically-conductive waveguide face of a stripe shape opposing the electrically conductive surface, the waveguide member extending along the electrically conductive surface; and an artificial magnetic conductor extending on both sides of the waveguide member. The waveguide member has a bend at which the direction that the waveguide member extends changes. A waveguide which is defined by the electrically conductive surface, the waveguide face, and the artificial magnetic conductor includes a gap enlargement where a gap between the electrically conductive surface and the waveguide face is locally increased. In a perspective view along a direction perpendicular to the electrically conductive surface, at least a portion of the bend has an overlap with the gap enlargement.