A circuit board that can decrease thermal stress acting between a semiconductor element and a board in association with temperature alteration and has high mechanical strength (rigidity) as a whole board (including a multilayer wiring layer) is provided. Ceramic base material having a coefficient of thermal expansion close to that of a semiconductor element and inner layer wiring are integrally sintered, and the circuit board is configured so that fine-lined conductor structure corresponding to a multilayer wiring layer in the inner layer wiring has predetermined width, intralayer interval and interlayer interval. Thereby, thermal stress acting between a semiconductor element and the board when the board is exposed to temperature alteration in a condition where it is joined with the semiconductor element is suppressed, rigidity of the board is maintained, and its reliability against temperature cycle is increased.