A heat pump hot-water heater comprising: a refrigerant circuit configured by connecting a compressor, a water-cooling medium heat exchanger, a pressure-reducing device, and an evaporator; a heating medium circulating circuit in which a heating medium heated by the water-cooling medium heat exchanger circulates; and a circulation pump that is arranged in the heating medium circulating circuit and conveys the heating medium, wherein the refrigerant circuit and the heating medium circulating circuit are provided in one exterior casing, characterized in that the heating medium circulating circuit is provided with a filter that collects impurities, and the exterior casing has an opening provided at a position facing the filter, and an opening and closing plate that covers the opening and that is attached to or detached from the exterior casing, wherein the heat pump hot-water heater further comprises a filter mounting part to which the filter is mounted, wherein a first heating medium pipe and a second heating medium pipe that constitute the heating medium circulating circuit are connected to a first end part and a second end part of the filter mounting part, respectively, the first heating medium pipe and the second heating medium pipe are pressure fitted and connected to the filter mounting part coaxially in series, the filter mounting part includes a filter storage part that stores the filter and a heating medium flow passage in which the heating medium flows, the filter storage part protrudes from the heating medium flow passage, and the filter storage part is positionable at an opening side of the exterior casing by rotating the filter mounting part with respect to the first heating medium pipe and the second heating medium pipe. a refrigerant circuit configured by connecting a compressor, a water-cooling medium heat exchanger, a pressure-reducing device, and an evaporator; a heating medium circulating circuit in which a heating medium heated by the water-cooling medium heat exchanger circulates; and a circulation pump that is arranged in the heating medium circulating circuit and conveys the heating medium, wherein the refrigerant circuit and the heating medium circulating circuit are provided in one exterior casing, characterized in that the heating medium circulating circuit is provided with a filter that collects impurities, and the exterior casing has an opening provided at a position facing the filter, and an opening and closing plate that covers the opening and that is attached to or detached from the exterior casing, wherein the heat pump hot-water heater further comprises a filter mounting part to which the filter is mounted, wherein a first heating medium pipe and a second heating medium pipe that constitute the heating medium circulating circuit are connected to a first end part and a second end part of the filter mounting part, respectively, the first heating medium pipe and the second heating medium pipe are pressure fitted and connected to the filter mounting part coaxially in series, the filter mounting part includes a filter storage part that stores the filter and a heating medium flow passage in which the heating medium flows, the filter storage part protrudes from the heating medium flow passage, and the filter storage part is positionable at an opening side of the exterior casing by rotating the filter mounting part with respect to the first heating medium pipe and the second heating medium pipe.