A glass ceramic sintered body having a small dielectric loss in a high frequency band of 10 GHz or higher and stable characteristics against temperature variation and a wiring substrate using the same are provided. The glass ceramic sintered body contains crystallized glass, an alumina filler, silica, and strontium titanate. The content of the crystallized glass is 50 mass % to 80 mass %, the content of the alumina filler is 15.6 mass % to 31.2 mass % in terms of Al2O3, the content of silica is 0.4 mass % to 4.8 mass % in terms of SiO2, and the content of the strontium titanate is 4 mass % to 14 mass % in terms of SrTiO3.