To provide a polyalkylene glycol-based refrigerant oil for refrigerators using ammonia as a refrigerant. The present invention provides a lubricant for refrigerators using ammonia refrigerant, comprising polyethers selected from the group consisting of a polyether represented by the following general formula (1) X—{—O—(AO)n—H}p  (1) (wherein X is a residue of a monool or polyol from which a hydroxyl group is eliminated; (AO)n is a polyoxyalkylene group formed by copolymerization of EO and an AO having 3 or more carbon atoms; n is 2 or more; and p is a valence of X) and having 50% or more of secondary hydroxyl groups among the hydroxyl groups located at the terminal of the structure based on the total hydroxyl groups, or a polyether represented by the following general formula (2) X—{—O—(AO1)a—(AO2)b—H}p  (2) (wherein X is a residue of a monool or polyol from which a hydroxyl group is eliminated; (AO1)n is a polyoxyalkylene group formed by copolymerization of ethylene oxide and propylene oxide and/or butylene oxide; AO2 is an oxyalkylene group having 3 or more carbon atoms; a is 2 or more; b is 1 or more; and p is a valence of X).