This paper discusses 400 Mbit/s optical regenerator integrated circuits, focusing on their circuit architecture and performance, and describes their application to a 400 Mbit/s optical regenerator. The basic design concepts for high-speed regenerator IC's are discussed and a new integrated circuit architecture based on these design concepts is proposed. The proposed architecture of regenerator IC's is used to fabricate five IC chips (Reshaping IC, Retiming IC, Decision IC, LD driver IC, and dc-to-dc converter IC) using a high-speed bipolar process with transistors having a unity gain bandwidth of 5 GHz. The combination of these IC's can achieve submarine and terrestrial long-haul optical transmission at bit rates up to 450 Mbits/s. These IC's are applied to a 400 Mbit/s IC optical regenerator. Experimental results show that the IC optical regenerator has an optical dynamic range of more than 27 dB without any adjustment and received average optical power required to maintain a 10-11error rate is less than -38 dBm. Experimental results fully satisfy the system requirements, and the feasibility of commercial application is demonstrated.