A regenerator for use in an ammonia absorption refrigerator comprises a heater for heating an ammonia aqueous solution and a rectifying column for enriching ammonia in an ammonia solution-vapor mixture obtained in and introduced from the heater, wherein the heater comprises a heater body having a heating chamber, a burner of lean pre-mixture combustion type disposed in a lower portion of the heating chamber, and a heat transfer tube bundle provided in a meandering arrangement above the burner within the heating chamber, the heat transfer tube bundle having an inlet and an outlet which are respectively connected to lower portions of the rectifying column via transfer pipes.