Provided is a process by which ammonia can be synthesized from nitrogen (which is a sustainable source) with resource conservation and reduced energy consumption. Specifically provided is a process wherein ammonia is synthesized using nitrogen and water as the raw materials by a thermochemical cycle with a renewable energy source. The process comprises, as a thermodynamically proceeding cycle, a step of forming ammonia via an ammonium halide by reaction of nitrogen with a hydrogen halide, while recycling the halogen generated as a by-product for the regeneration of a hydrogen halide. Thus, ammonia can be synthesized without an auxiliary material.