[Problem] The aim of the present invention lies in providing a glass ceramic sintered compact in which dielectric loss in a high-frequency region is reduced, without any reduction in sintering density, and also in providing a wiring board employing same. [Solution] A glass ceramic sintered compact containing a glass component, a ceramic filler and a composite oxide, characterized in that the glass component is crystallized glass on which is deposited a diopside oxide crystal phase including at least Mg, Ca and Si, and the composite oxide includes at least Al and Co.