A ceramic circuit board having a metal circuit board adhered onto an alumina substrate, wherein the alumina substrate contains 94-98 mass% of alumina (Al2O3) and 2-6 mass% of a sintering aid-derived component generated from a sintering aid admixed before sintering, the sintering aid-derived component is an inorganic oxide containing silicon, the silicon in terms of silica (SiO2) in the sintering aid-derived component is contained at 0.01-1.5 mass% for every 100 mass% of the alumina substrate, and the alumina substrate has a maximum void size of no greater than 15 [mu]m, an average void size of no greater than 10 [mu]m, and a Vickers hardness of at least 1300.