Optical waveguide forming resin composition, optical waveguide forming resin film, and optical waveguide using these, and method for producing same

The present invention pertains to an optical waveguide forming resin composition containing: (A) a polymer having an alkali-soluble group; (B) a compound having an ethylenically unsaturated group within the molecule thereof; and (C) a polymerization initiator, wherein component (B) contains at least one compound selected from (B1-1) to (B1-3) as component (B1), and a compound having, within the molecule thereof, an ethylenically unsaturated group and a group that reacts with the alkali-soluble group of component (A) as component (B2). (B1-1): A compound having three or more ethylenically unsaturated groups. (B1-2): A compound having a carboxy group and two or more ethylenically unsaturated groups. (B1-3): A compound having a urethane bond and one or more ethylenically unsaturated groups.