PURPOSE: To manufacture an IR optical fiber superior in mechanical strength, durability, and permeability by coating the outer circumference of a core made of a metallic halide type compd. with a heated and softened chalcogenide compd. to form a clad part.

CONSTITUTION: A metallic halide type compd. A, such as AgBr, is contained in the container 1 of an extrusion molding machine is pressed with a stem 3, and extrusion molded through the opening 4 of a die 3 to form the core 6 of an IR optical fiber 5. This is introduced into a chalcogenide compd. 11, such as Ge.S, fed from a feeding port 10 into a softening container 7 and made viscous like starch syrup with a heater 8 to coat the outer circumference of the core 6, and a clad part 16 is formed after cooling, thus obtaining an IR optical fiber 5 of a step index type.