A base disk is provided by a rapidly-solidified aluminum alloy whose major component is Si, wherein the rapidly-solidified aluminum alloy includes 15wt%-40wt% of the Si, 0.5wt%-6wt% of Cu, 0.2 wt%-3wt% of Mg, and the remaining which is constituted principally by aluminum. The rapidly-solidified aluminum alloy includes Si particles whose average diameter is not larger than 5µm and has a porosity not larger than 1 vol%. The ratio of a tensile strength of the base disk to a specific gravity of the base disk (tensile strength [MPa] / specific gravity) is not smaller than 90, and the ratio of a fatigue strength of the base disk to the specific gravity of the base disk (fatigue strength [MPa] / specific gravity) is not smaller than 30. A multiplicity of the base disks can be produced at a time through a single process of producing the alloy, thereby leading to a reduced producing cost. Further, the high content of Si in the aluminum alloy increases elastic modulus of the base disk, whereby the elastic elongation and deformation of the base disk due to generation of centrifugal force are minimized during rotation of the base disk at a high peripheral speed, and accordingly the abrasive layer is advantageously prevented from being separated from the base disk. Further, the small particles of Si each having a size not larger than 5µm are deposited and distributed evenly over the entirety of the aluminum alloy, so that the aluminum alloy has a high degree of strength in its entirety with a high degree of stability, preventing the aluminum alloy from being brittle and thereby preventing the strength of the aluminum alloy from being reduced, so that the aluminum alloy has a high degree of strength in its entirety with a high degree of stability. Still further, the aluminum alloy has a porosity not larger than 1 vol%, thereby increasing the strength of the aluminum alloy, and improving its resistance to a grinding fluid. Still further, the base disk has a higher stability in its strength, owing to the increased ratio of the tensile strength to the specific gravity and the increased ratio of the fatigue strength to the specific gravity, thereby permitting the base disk to be used for a longer time and to be reutilized for a longer period. Still further, the base disk provided by the aluminum alloy can be reutilized without being discarded, thereby proving an environmental advantage.