Refrigerant Quantity Diagnosis Device, Refrigerant System, and Refrigerant Quantity Diagnosis Method

A refrigerant quantity diagnosis device includes: an evaluation value calculation part that calculates a refrigerant quantity index evaluation value including a ratio of a measured refrigerant quantity index value to a reference refrigerant quantity index value in each of a normal period and a determination period; and a refrigerant quantity diagnosis part that diagnoses a refrigerant quantity based on the refrigerant quantity index evaluation value. The evaluation value calculation part calculates a first refrigerant quantity index evaluation value in the normal period and a second refrigerant quantity index evaluation value in the determination period, based on respective reference refrigerant quantity index values having respective values associated with an operating condition of interest, and respective measured refrigerant quantity index values. The refrigerant quantity diagnosis part compares information on the first refrigerant quantity index evaluation value with that on the second one and thereby diagnoses the refrigerant quantity.