In a multilayered ceramic substrate having a ceramic substrate fireable in low temperatures and a metal member for input/output brazed to the ceramic substrate, an intermediate layer including a ceramic component is arranged between the ceramic substrate and the metal member in such a manner that thermal coefficients .alpha..sub.1, .alpha..sub.2 and .alpha..sub.3 between a room temperature and near a brazing temperature of the metal member, the ceramic component in the intermediate layer and the ceramic layer, respectively, maintains a relation of .alpha..sub.1 >.alpha..sub.2 >.alpha..sub.3. Moreover, the ceramic substrate fireable in low temperatures is constructed by first ceramic layer having a flexural strength more than 25 kg/mm.sup.2 and a second ceramic layer having a dielectric constant less than 7. In these constructions, the multilayered ceramic substrate having a sufficient adhesion strength between the metal member and the ceramic substrate and a good reliability can be obtained, while advantages of the ceramic substrate fireable in low temperatures can be maintained.