A heat-pump hot water generator, comprising: a refrigerant circuit formed by annularly connecting, to one another, a compressor, a radiator in which refrigerant and heating medium exchange heat, decompressing means and an evaporator through a refrigerant pipe; a control means configured to execute a plurality of operation modes; and a heating medium path through which the heating medium flows, wherein a main path having the radiator and an auxiliary path having heat storage means which exchanges heat with the heating medium are provided in the heating medium path in parallel, characterized in that the heat-pump hot water generator further comprises: a heat storing path which branches off from the refrigerant circuit placed in a discharge side of the compressor, and which is connected to the refrigerant circuit through the heat storage means, a solenoid valve arranged to stop flow of the refrigerant to the heat storing path, and arranged such that if the solenoid valve is opened, the refrigerant which is discharged from the compressor flows through the heat storage means into the radiator and if the solenoid valve is closed, the refrigerant which is discharged from the compressor flows into the radiator without flowing through the heat storage means, wherein the plurality of operation modes executed by the control means includes a first operation mode configured for heating the heating medium by the radiator, a second operation mode configured for heating the heating medium by the heat storage means, and a defrosting operation mode, wherein, in the defrosting operation mode, the heating medium is heated by the heat storage means according to the second operation mode, and the flow of the refrigerant to the heat storing path is stopped by the solenoid valve, whereby high temperature and high pressure refrigerant from the compressor is made to flow through the evaporator. a refrigerant circuit formed by annularly connecting, to one another, a compressor, a radiator in which refrigerant and heating medium exchange heat, decompressing means and an evaporator through a refrigerant pipe; a control means configured to execute a plurality of operation modes; and a heating medium path through which the heating medium flows, wherein a main path having the radiator and an auxiliary path having heat storage means which exchanges heat with the heating medium are provided in the heating medium path in parallel, characterized in that the heat-pump hot water generator further comprises: a heat storing path which branches off from the refrigerant circuit placed in a discharge side of the compressor, and which is connected to the refrigerant circuit through the heat storage means, a solenoid valve arranged to stop flow of the refrigerant to the heat storing path, and arranged such that if the solenoid valve is opened, the refrigerant which is discharged from the compressor flows through the heat storage means into the radiator and if the solenoid valve is closed, the refrigerant which is discharged from the compressor flows into the radiator without flowing through the heat storage means, wherein the plurality of operation modes executed by the control means includes a first operation mode configured for heating the heating medium by the radiator, a second operation mode configured for heating the heating medium by the heat storage means, and a defrosting operation mode, wherein, in the defrosting operation mode, the heating medium is heated by the heat storage means according to the second operation mode, and the flow of the refrigerant to the heat storing path is stopped by the solenoid valve, whereby high temperature and high pressure refrigerant from the compressor is made to flow through the evaporator. a heat storing path which branches off from the refrigerant circuit placed in a discharge side of the compressor, and which is connected to the refrigerant circuit through the heat storage means, a solenoid valve arranged to stop flow of the refrigerant to the heat storing path, and arranged such that if the solenoid valve is opened, the refrigerant which is discharged from the compressor flows through the heat storage means into the radiator and if the solenoid valve is closed, the refrigerant which is discharged from the compressor flows into the radiator without flowing through the heat storage means, wherein the plurality of operation modes executed by the control means includes a first operation mode configured for heating the heating medium by the radiator, a second operation mode configured for heating the heating medium by the heat storage means, and a defrosting operation mode, wherein, in the defrosting operation mode, the heating medium is heated by the heat storage means according to the second operation mode, and the flow of the refrigerant to the heat storing path is stopped by the solenoid valve, whereby high temperature and high pressure refrigerant from the compressor is made to flow through the evaporator.