Abstract: The 120~130mm diameter horizontal continuous caster in Keihin Works, NKK was revamped to realize rational supply of billets for seamless pipe. A moveable multi-stage electromagnetic stirrer and an on-line slow cooling furnace were added, and the breakring material and the mould configuration were improved. Therefore the product size range was enlarged to 370mm diameter, steel grades was expanded to such high-alloyed steel as SUS420J1 and also the cast billet quality improved.