A heat treatment method for heat-treating an alloy that undergoes multiple-step transformation with temperature, the alloy being selected from the group consisting of: 300 series stainless steel; 600 series stainless steel; 2000 series aluminum alloys; 6000 series aluminum alloys; 7000 series aluminum alloys; copper alloys, the method comprising: a preliminary-state-generating step of heat-treating the alloy by bringing the alloy in contact with a contact-type heating element for 0.01 sec or more and 3.0 sec or less, the contact-type heating element being adjusted to a temperature within a preliminary-state-generating temperature region determined on the basis of a first temperature related to a first transformation of the alloy and a second temperature, which is higher than the first temperature, related to a second transformation of the alloy so as to generate a preliminary state in the alloy, wherein: the first temperature is determined by differential scanning calorimetry and is selected from: (i) a temperature at which the first transformation begins, corresponding to the temperature at the rising edge of the peak, (ii) a temperature at which the first transformation becomes most active, corresponding to the temperature at the peak temperature, and (iii) a temperature at which the first transformation ends, corresponding to the temperature at which the peak is passed and becomes flat or the temperature immediately before the rising edge of the next peak, and the second temperature is determined by differential scanning calorimetry and is selected from: (iv) a temperature at which the second transformation begins, corresponding to the temperature at the rising edge of the peak, (v) a temperature at which the second transformation becomes most active, corresponding to the temperature at the peak temperature, and (vi) a temperature at which the second transformation ends, corresponding to the temperature at which the peak is passed and becomes flat or the temperature immediately before the rising edge of the next peak, and wherein the preliminary-state-generating temperature region is a temperature region higher than the first temperature and lower than the second temperature. a preliminary-state-generating step of heat-treating the alloy by bringing the alloy in contact with a contact-type heating element for 0.01 sec or more and 3.0 sec or less, the contact-type heating element being adjusted to a temperature within a preliminary-state-generating temperature region determined on the basis of a first temperature related to a first transformation of the alloy and a second temperature, which is higher than the first temperature, related to a second transformation of the alloy so as to generate a preliminary state in the alloy, wherein: the first temperature is determined by differential scanning calorimetry and is selected from: (i) a temperature at which the first transformation begins, corresponding to the temperature at the rising edge of the peak, (ii) a temperature at which the first transformation becomes most active, corresponding to the temperature at the peak temperature, and (iii) a temperature at which the first transformation ends, corresponding to the temperature at which the peak is passed and becomes flat or the temperature immediately before the rising edge of the next peak, and (i) a temperature at which the first transformation begins, corresponding to the temperature at the rising edge of the peak, (ii) a temperature at which the first transformation becomes most active, corresponding to the temperature at the peak temperature, and (iii) a temperature at which the first transformation ends, corresponding to the temperature at which the peak is passed and becomes flat or the temperature immediately before the rising edge of the next peak, and the second temperature is determined by differential scanning calorimetry and is selected from: (iv) a temperature at which the second transformation begins, corresponding to the temperature at the rising edge of the peak, (v) a temperature at which the second transformation becomes most active, corresponding to the temperature at the peak temperature, and (vi) a temperature at which the second transformation ends, corresponding to the temperature at which the peak is passed and becomes flat or the temperature immediately before the rising edge of the next peak, (iv) a temperature at which the second transformation begins, corresponding to the temperature at the rising edge of the peak, (v) a temperature at which the second transformation becomes most active, corresponding to the temperature at the peak temperature, and (vi) a temperature at which the second transformation ends, corresponding to the temperature at which the peak is passed and becomes flat or the temperature immediately before the rising edge of the next peak,