A conceptual study was made for the actinide transmutation system which consists of a subcritical core and a 1.5 GeV proton accelerator. In this system, the actinide nuclides are transmuted by fast fission. In order to make neutron spectrum hard, metallic alloy fuels are installed and are cooled with liquid metal sodium in the core. Tungsten target was also employed to suppress the power peaking which is induced by incident protons. The performance of the subcritical core was estimated for the case in which the effective multiplication factor is about 0.90.