A method for replacement of a part of a refrigeration cycle apparatus including a compressor that compresses a flammable refrigerant, a condenser that condenses the refrigerant by heat exchange, an expansion device (16a, 16b, 16c) that controls a pressure of the condensed refrigerant, and an evaporator that exchanges heat between the pressure-reduced refrigerant and air to evaporate the refrigerant, the compressor, the condenser, the expansion device (16a, 16b, 16c), and the evaporator being connected by pipes to form a refrigerant circuit, the method comprising: a refrigerant recovery step of allowing the refrigerant to flow out of the refrigerant circuit through a container connecting device; a pressure reduction step of connecting a pressure reducing device to the container connecting device to reduce a pressure in the refrigerant circuit through the container connecting device such that the pressure in the refrigerant circuit becomes equal to or less than a set pressure or until a time equal to or greater than a setting time elapses; and a part replacement step of removing the part from the refrigerant circuit by heating to replace the part, wherein the refrigerant is a refrigerant mixture containing at least two flammable refrigerants which serve as a first refrigerant component and a second refrigerant component and the set pressure is a pressure less than a value expressed by (LFL1 × a percentage of the first refrigerant component + LFL2 × a percentage of the second refrigerant component) × 1000 × R × T/(M1 x the percentage of the first refrigerant component + M2 × the percentage of the second refrigerant component) (Pa) where M1 (g/mol) and M2 (g/mol) denote molecular weights of the first and second refrigerant components, respectively, R (Pa × L/K × mol) denotes a gas constant, T denotes a typical temperature of the refrigerant in the refrigerant circuit, which is a temperature of ambient air after stop of an operation of the refrigerant cycle apparatus or a temperature in the evaporator just after stop of the operation of the refrigerant cycle apparatus, and LFL1 (kg/m3) and LFL2 (kg/m3) denote lower flammability limits of the first and second refrigerant components, respectively. a refrigerant recovery step of allowing the refrigerant to flow out of the refrigerant circuit through a container connecting device; a pressure reduction step of connecting a pressure reducing device to the container connecting device to reduce a pressure in the refrigerant circuit through the container connecting device such that the pressure in the refrigerant circuit becomes equal to or less than a set pressure or until a time equal to or greater than a setting time elapses; and a part replacement step of removing the part from the refrigerant circuit by heating to replace the part, wherein the refrigerant is a refrigerant mixture containing at least two flammable refrigerants which serve as a first refrigerant component and a second refrigerant component and the set pressure is a pressure less than a value expressed by (LFL1 × a percentage of the first refrigerant component + LFL2 × a percentage of the second refrigerant component) × 1000 × R × T/(M1 x the percentage of the first refrigerant component + M2 × the percentage of the second refrigerant component) (Pa) where M1 (g/mol) and M2 (g/mol) denote molecular weights of the first and second refrigerant components, respectively, R (Pa × L/K × mol) denotes a gas constant, T denotes a typical temperature of the refrigerant in the refrigerant circuit, which is a temperature of ambient air after stop of an operation of the refrigerant cycle apparatus or a temperature in the evaporator just after stop of the operation of the refrigerant cycle apparatus, and LFL1 (kg/m3) and LFL2 (kg/m3) denote lower flammability limits of the first and second refrigerant components, respectively.