A mixture of a urethane monomer and a urethane oligomer having a group represented in Fig. 4 and a polymerization initiator, which is a precursor of an elastomer exhibiting a flexural modulus of elasticity of 1,000 MPa or less after curing, is used as a clad material. The clad material is applied on a base plate and is pressed from above by a stamper and is spread into a thin film. After the clad material is cured to form an under clad layer, a core is formed on the under clad layer. Then, the above clad material is applied on the under clad layer, is pressed by a stamper from above and is spread into a thin film. The latter clad material is cured to form an upper clad layer. Finally, the base plate is removed, and a film optical waveguide capable of being bent with a small radius of curvature is obtained.