To provide an ammonia absorption type refrigerating machine and its corrosion inhibitor superior in environmental protection and capable of sufficiently preventing corrosion of devices of a refrigerating system even in a fluidized state and a boiled state of an ammonia aqueous solution.

The ammonia absorption type refrigerating machine includes a refrigerating system composed of an evaporator 1, an absorber 2, a generator 7, a rectifier 6, a condenser 8 and the like, and the ammonia aqueous solution filled in the refrigerating system. Ammonium molybdenum acid and zinc hydroxide are included in the ammonia aqueous solution.