A rail car air-conditioning device comprising: a refrigerant circuit comprising (i) a compressor to compress a refrigerant and (ii) an outside air heat exchanger to perform heat exchange between the refrigerant and outside air; a blower to blow the outside air into the outside air heat exchanger; a compressor operation frequency deriver to, based on a setting temperature and a rail car interior temperature, derive a compressor operation frequency of the compressor; a compressor driver to drive the compressor at the compressor operation frequency derived by the compressor operation frequency deriver; the device characterised by: a blower operation frequency deriver to derive, in accordance with a predetermined correspondence relationship, a blower operation frequency of the blower corresponding to the compressor operation frequency derived by the compressor operation frequency deriver; and a blower driver to drive the blower at the blower operation frequency derived by the blower operation frequency deriver, wherein the blower operation frequency deriver sets the correspondence relationship by selection of one mode from among multiple modes that include at least a first operation mode and a second operation mode, in the first operation mode, an energy efficiency of the refrigerant circuit relative to the compressor operation frequency is higher than that of the second operation mode, and the blower operation frequency corresponding to the compressor operation frequency is higher than the blower operation frequency corresponding to the same compressor operation frequency when prescribed in the second operation mode, and in the second operation mode, the blower operation frequency increases as the compressor operation frequency increases, and the blower operation frequency corresponding to the compressor operation frequency is lower than the blower operation frequency corresponding to the same compressor operation frequency when prescribed in the first operation mode. a refrigerant circuit comprising (i) a compressor to compress a refrigerant and (ii) an outside air heat exchanger to perform heat exchange between the refrigerant and outside air; a blower to blow the outside air into the outside air heat exchanger; a compressor operation frequency deriver to, based on a setting temperature and a rail car interior temperature, derive a compressor operation frequency of the compressor; a compressor driver to drive the compressor at the compressor operation frequency derived by the compressor operation frequency deriver; the device characterised by: a blower operation frequency deriver to derive, in accordance with a predetermined correspondence relationship, a blower operation frequency of the blower corresponding to the compressor operation frequency derived by the compressor operation frequency deriver; and a blower driver to drive the blower at the blower operation frequency derived by the blower operation frequency deriver, wherein the blower operation frequency deriver sets the correspondence relationship by selection of one mode from among multiple modes that include at least a first operation mode and a second operation mode, in the first operation mode, an energy efficiency of the refrigerant circuit relative to the compressor operation frequency is higher than that of the second operation mode, and the blower operation frequency corresponding to the compressor operation frequency is higher than the blower operation frequency corresponding to the same compressor operation frequency when prescribed in the second operation mode, and in the second operation mode, the blower operation frequency increases as the compressor operation frequency increases, and the blower operation frequency corresponding to the compressor operation frequency is lower than the blower operation frequency corresponding to the same compressor operation frequency when prescribed in the first operation mode.