A manufacturing method for a waveguide includes forming a core including a first and a second layer. The first layer has a top surface including a first region opposed to a bottom surface of the second layer, and a second region not opposed to the bottom surface of the second layer. Forming the core includes a step of forming an initial first layer, an etching stopper layer on the second region of the top surface of the initial first layer, an initial second layer on the initial first layer and the etching stopper layer, and a step of etching the initial second layer until the etching stopper layer is exposed, to make the initial second layer into the second layer. A difference between the refractive index of the etching stopper layer and the core is smaller than or equal to 10% of the refractive index of the core.