PROBLEM TO BE SOLVED: To provide a silico-alumino-phosphate of an AFX structure that is used under a moisture containing environment and further that exhibits a high catalytic activity as a nitrogen oxide reduction catalyst.SOLUTION: Provided is a silico-alumino-phosphate of an AFX structure that has a solid acid amount of 0.90 mmol/g or more and contains copper. The silico-alumino-phosphate of the AFX structure containing copper can be obtained by a production method characterized in that it has a mixing step of mixing the silico-alumino-phosphate of the AFX structure and copper containing alcohol.