A process for producing a polymer optical waveguide, including the steps of: preparing a mold; bringing into close contact with a cladding substrate which has good adhesiveness to the mold; introducing, by capillarity, a curable resin; and curing the introduced curable resin, wherein one through hole or multiple through holes arranged at regular intervals in a longitudinal direction of the core portion are opened to form the one or more resin input ports or one or more resin output ports in order for both the cut ends to be used as resin output portions; and after the curable resin is introduced into the concave portion, a resin pushing member is inserted into each of the one or more resin input ports and/or the one or more resin output ports, to thereby perform the step of introducing the curable resin into the concave portion of the mold by capillarity.