A heat pump apparatus comprising: an outdoor unit comprising a first compressor to compress a first refrigerant, a first heat exchanger to cause a heat exchange to occur between the first refrigerant and outdoor air, and a first expansion valve to expand the first refrigerant; an indoor unit comprising a second heat exchanger to cause a heat exchange to occur between the first refrigerant and indoor air, and a second expansion valve to expand the first refrigerant; a hydro unit comprising a second compressor to compress a second refrigerant, a third heat exchanger to cause a heat exchange to occur between the first refrigerant and the second refrigerant, a fourth heat exchanger to cause a heat exchange to occur between the first refrigerant and water, a fifth heat exchanger to cause a heat exchange to occur between the second refrigerant and water, a third expansion valve to expand the first refrigerant and arranged between the third heat exchanger and the second expansion valve, and a fourth expansion valve to expand the first refrigerant and arranged between the fourth heat exchanger and the second expansion valve, and a fifth expansion valve to expand the second refrigerant; a refrigerant flow path switching unit (112a - d) to switch among flow paths of the first refrigerant between the first compressor and the first heat exchanger, between the first compressor and the second heat exchanger, between the first compressor and the third heat exchanger, and between the first compressor and the fourth heat exchanger; and a water flow path switching unit to switch between flow paths of the water to allow the water to flow to one of the fourth heat exchanger and the fifth heat exchanger. an outdoor unit comprising a first compressor to compress a first refrigerant, a first heat exchanger to cause a heat exchange to occur between the first refrigerant and outdoor air, and a first expansion valve to expand the first refrigerant; an indoor unit comprising a second heat exchanger to cause a heat exchange to occur between the first refrigerant and indoor air, and a second expansion valve to expand the first refrigerant; a hydro unit comprising a second compressor to compress a second refrigerant, a third heat exchanger to cause a heat exchange to occur between the first refrigerant and the second refrigerant, a fourth heat exchanger to cause a heat exchange to occur between the first refrigerant and water, a fifth heat exchanger to cause a heat exchange to occur between the second refrigerant and water, a third expansion valve to expand the first refrigerant and arranged between the third heat exchanger and the second expansion valve, and a fourth expansion valve to expand the first refrigerant and arranged between the fourth heat exchanger and the second expansion valve, and a fifth expansion valve to expand the second refrigerant; a refrigerant flow path switching unit (112a - d) to switch among flow paths of the first refrigerant between the first compressor and the first heat exchanger, between the first compressor and the second heat exchanger, between the first compressor and the third heat exchanger, and between the first compressor and the fourth heat exchanger; and a water flow path switching unit to switch between flow paths of the water to allow the water to flow to one of the fourth heat exchanger and the fifth heat exchanger.