A sulfide solid electrolyte that can suppress the generation of hydrogen sulfide gas while maintaining the lithium ion conductivity; and an electrode composite material, a slurry and a battery, in each of which the sulfide solid electrolyte is used, are provided. The sulfide solid electrolyte contains lithium (Li), phosphorus (P) and sulfur (S) elements; at least one halogen (X) element; and at least one metal (M) element having a first ionization energy of more than 520.2 KJ/mol and less than 1007.3 KJ/mol, wherein, in an X-ray diffraction pattern measured with CuKα1 radiation, peaks are present at positions of 2θ=25.19°±1.00° and 29.62°±1.00°.