C-band (5712-MHz) linac is used as the main accelerator of the Japanese X-ray free electron laser (XFEL) facility in SPring-8. Since the C-band linac has high acceleration gradient, our 8-GeV accelerator is compact. One C-band unit consists of following components; two choke-mode-type 1.8-m accelerating structures, an rf pulse compressor, a 50-MW klystron, and a 110-MW compact modulator power supply. We will use 64 units of them for the X-FEL accelerator. Since November 2005, we have operated two C-band units in the SCSS (SPring-8 Compact SASE Source) 250-MeV accelerator. After rf conditioning, the accelerating gradient was achieved to 35-MV/m. We successfully accelerated the electron beam by this gradient of electrical field.