Provided is an optical waveguide element including spot size conversion means with suppressed optical insertion loss without complicating a manufacturing process. An optical waveguide element includes an optical waveguide substrate (4) having a rib-type optical waveguide (10) formed of a material having an electro-optic effect, and spot size conversion means for changing a mode field diameter of a light wave propagating through the optical waveguide at a position where an input end or an output end of the rib-type optical waveguide (10) is formed, in which the spot size conversion means includes a first configuration layer (1) that is connected to the rib-type optical waveguide (10) and includes a tapered portion (11) in which a width of the optical waveguide expands, a second configuration layer (2) that is laminated on the first configuration layer (1) and has a width narrower than a width of the first configuration layer (1), and a third configuration layer (3) that is disposed to cover the second configuration layer (2) excluding a part of the second configuration layer (2) close to the rib-type optical waveguide and has a width wider than the width of the second configuration layer (2).