This paper proposes an effective field-programmable gate array (FPGA) implementation of a successive-cancellation (SC) decoder for polar codes that have recently attracted attention as error-correcting codes adopted for 5G wireless systems. We focus on effective ways of partitioning the SC decoding procedure into combinational and sequential logic parts. It can be shown that the SC decoder of length N(= N1N2) can be divided into two parts: N1 SC decoders of length N2 and a single SC decoder of length N1. While the N1 decoders in the first part can perform in parallel, the decoding procedure in the second part is performed sequentially, which causes a bottleneck due to a long latency. We present an SC decoder architecture in which the first part is implemented using sequential logic circuits, and the second part is implemented using only combinational logic circuits. The overall latency and clock frequency of the decoder are balanced by the divisor N1 of N, and we show that an appropriate choice of N1 yields an efficient implementation with a high throughput. We demonstrate an FPGA implementation of the decoder architecture for a 1024-bit-length polar code and show that our FPGA decoder can achieve three times higher throughput than the conventional sequential semi-parallel decoder without significantly increasing the hardware resources.