The purpose of the present invention is to inexpensively provide a heat pump device in which HFO-1123 circulates. This heat pump device in which a refrigerant circulates between an indoor unit and an outdoor unit is characterized in that: the refrigerant is a refrigerant mixture of HFO-1123 and an HFC series refrigerant that is not HFO-1123; the cooling capacity (kW) of the outdoor unit is 2.2 kW - 9.5 kW inclusive; the outer diameter (φ) (mm) of a gas pipe connecting the indoor unit and the outdoor unit and the cooling capacity (kW) of the outdoor unit satisfy a relational expression (1.00 ≤ gas pipe outer diameter (φ) (mm) / outdoor unit cooling capacity (kW) ≤ 5.77); and the outer diameter (φ) (mm) of a fluid pipe connecting the indoor unit and the outdoor unit and the cooling capacity (kW) of the outdoor unit satisfy a relational expression (0.67 ≤ fluid pipe outer diameter (φ) (mm) / outdoor unit cooling capacity (kW) ≤ 5.77).
