To obtain excellent lubricity hardly causing fuzzing or yarn breakage in a yarn manufacturing process by applying a specific organic phosphoric ester compound as a lubricant to a synthetic fiber for industrial materials.

One or more organic phosphoric ester compounds selected from among acid phosphoric esters (salts) represented by formulae I and II [X1 and X2 are each a group represented by formulae III and IV; R1, R2, R3 and R4 are each an 8-30C alkyl or an 8-30C alkenyl; A1 and A2 are each a 2-4C alkylene; (p), (q), (r) and (s) are each an integer of 3-20; (m) and (n) are each an integer of 1-20] are used as a lubricant and heated at 40-80°C. The resultant heated compounds in a neat state in an amount of 0.1-3wt.% are applied to a synthetic fiber for industrial materials in a step after spinning thereof to drawing to thereby manifest excellent lubricity even when yarns are manufactured at high temperatures under high contact pressures.