Abstract: [OBJECTS] To provide an elastic strip material that has a cross-sectional shape suited to intended uses such as seals or cushions, as well as a method of and an apparatus for mass-producing the strip material efficiently and inexpensively. [MEANS FOR ACHIEVING THE OBJECTS] A heat setting composition is used whose main ingredients are a polyurethane prepolymer and a latent solidifier obtained by deactivating a solid polyamine. A compressed gas is dispersed throughout the composition to give a fluid mixture ‘a’, that is then foamed and heated to or above a critical temperature to solidify as the strip material. The fluid mixture ‘a’ is extruded from an extruder (1), guided into a liquid or gaseous heating zone (2), caused to solidify during travel within the zone, and shaped at the same time into a desired configuration before discharged from the zone (2).