PURPOSE: To prevent the migration of grease to the fixed part through the space around the inner core wires of a strand of a prestressing steel for partial unbonding use and prevent the lowering of the adhesivity of the fixing part to concrete.

CONSTITUTION: A lacquer coating film 2 having a thickness of 50μm is applied to the surface of the twist wires 1 of prestressing steel. The coating film 2 forms a dense layer on the outer circumference of the twist wires of prestressing steel to form a filling part having a triangular pyramidal cross-section in the groove 5 of twist pitch. A layer of rustproofing lubricating grease 3 is formed outside the coating film 2 and the outer circumference of the grease layer is surrounded by a flexible synthetic resin sheath 4.