A polymerase chain reaction method for performing a PCR process on a treatment target liquid using a microchannel apparatus including a microchannel chip and a heating/cooling control apparatus, the PCR method comprising: (a) preparing the microchannel apparatus including the microchannel chip and the heating/cooling control apparatus; the microchannel chip including: a first substrate layer comprising an introducing channel and a discharging channel; and a second substrate layer that is disposed on the first substrate layer and comprises a second substrate layer body and a metal film, the second substrate layer body comprising a microchannel connected to the introducing channel and the discharging channel, the microchannel being filled with the treatment target liquid, the metal film structuring an upper surface of the microchannel, the heating/cooling control apparatus including: a temperature regulator that is disposed so as to be in contact with the metal film of the second substrate layer and is capable of heating or cooling the metal film; a power source that applies voltage to the temperature regulator; and a heating/cooling controller that controls the voltage applied from the power source to the temperature regulator; (b) controlling, with the heating/cooling controller, the voltage applied from the power source to the temperature regulator so as to change a temperature of the treatment target liquid in the microchannel, thereby achieving the PCR process, wherein an end of the metal film of the second substrate layer in the microchannel chip is buried in the second substrate layer body. (a) preparing the microchannel apparatus including the microchannel chip and the heating/cooling control apparatus; the microchannel chip including: a first substrate layer comprising an introducing channel and a discharging channel; and a second substrate layer that is disposed on the first substrate layer and comprises a second substrate layer body and a metal film, the second substrate layer body comprising a microchannel connected to the introducing channel and the discharging channel, the microchannel being filled with the treatment target liquid, the metal film structuring an upper surface of the microchannel, the heating/cooling control apparatus including: a temperature regulator that is disposed so as to be in contact with the metal film of the second substrate layer and is capable of heating or cooling the metal film; a power source that applies voltage to the temperature regulator; and a heating/cooling controller that controls the voltage applied from the power source to the temperature regulator; a first substrate layer comprising an introducing channel and a discharging channel; and a second substrate layer that is disposed on the first substrate layer and comprises a second substrate layer body and a metal film, the second substrate layer body comprising a microchannel connected to the introducing channel and the discharging channel, the microchannel being filled with the treatment target liquid, the metal film structuring an upper surface of the microchannel, the heating/cooling control apparatus including: a temperature regulator that is disposed so as to be in contact with the metal film of the second substrate layer and is capable of heating or cooling the metal film; a power source that applies voltage to the temperature regulator; and a heating/cooling controller that controls the voltage applied from the power source to the temperature regulator; a temperature regulator that is disposed so as to be in contact with the metal film of the second substrate layer and is capable of heating or cooling the metal film; a power source that applies voltage to the temperature regulator; and a heating/cooling controller that controls the voltage applied from the power source to the temperature regulator; (b) controlling, with the heating/cooling controller, the voltage applied from the power source to the temperature regulator so as to change a temperature of the treatment target liquid in the microchannel, thereby achieving the PCR process,