A ceramic circuit board that protects a metallized wiring layer from fusion when a large electric current is applied thereto. The ceramic circuit board includes a ceramic substrate, a plurality of metallized wiring layers formed on the ceramic substrate, and a metal circuit plate made of copper, which is attached to part of the metallized wiring layers. The condition, S≧6×10−5i2, is fulfilled in the ceramic circuit board, whereby S (mm2) is the sectional area of the metal circuit plate and i (A) the value of a flowing electric current.