PURPOSE: To stabilize and uniformize the quality of a modified layer when build up is performed with the welding wire by developing a sheath material in a planar form, coating seed particles with coated particles to form capsule particles, sticking them to a sheath material, then, rounding it out in a wire form.

CONSTITUTION: A flat plate 1 made from the sheath material is developed in the form of a belt having a prescribed width. Powder of capsule particles is manufactured to fill this sheath material 1. Particles 3 being coated particles having the same material as the sheath material 1 are stuck to ceramic particles 2 making seed particles. Impact is given in the high speed air flow. As a result, the capsule particles 4 which are closely stuck to one another are obtained and composite fine particles (powder) 5 being the aggregate of the capsule particles are manufactured. Then, the composite fine particles 5 of these capsule particles 4 are mounted on the upper surface 6 making the inside of the planar sheath material 1 are joined and stuck by the ultrasonic joining method. Then. the sheath material 1 with the fine particles 5 is rounded out in the width direction, both its ends 8 are bent and joined to mantle the composite fine particles 5. In this way, the welding wire 9 whose inside is filled with the capsule particles 4 is manufactured.