A method of producing a polymer optical waveguide, including: preparing a mold; preparing a lower film base material; introducing a core-forming curable resin into a first through-hole of the mold with which the lower film base material is brought into close contact while sucking the concave portion of the mold from a second through-hole under reduced pressure to introduce the core-forming curable resin into the concave portion of the mold; curing the core-forming curable resin which has been introduced; removing the mold from the lower film base material; providing a clad-forming curable resin layer and an upper film base material, the clad-forming curable resin layer being sandwiched between the lower film base material, on which the core is formed, and the upper film base material; and curing the clad-forming curable resin layer to fix the lower film base material and the upper film base material.