In this paper, we propose a spectrum division & adaptive subcarrier allocation for cooperative amplify-and-forward (AF) relay using single carrier-frequency division multiple access (SC-FDMA). To obtain increased frequency diversity gain, the transmit SC signal spectrum is divided into sub-blocks, to each of which a different set of subcarriers (resource block) is adaptively allocated based on the each user's channel condition. The adaptive subcarrier allocation has a tradeoff between the channel capacity and the peak-to-average power ratio (PAPR). We evaluate the outage channel capacity of SC-FDMA using cooperative AF relay and discuss such a tradeoff relationship. Simulation results show that the SC-FDMA using the proposed spectrum division & the adaptive subcarrier allocation can achieve the similar capacity to the orthogonal frequency division multiple access (OFDMA) while keeping lower PAPR property.