This invention provides a constant temperature device, comprising: a flow guide, a temperature regulating device, and a
heat exchanger. The flow guide has a liquid flow channel for flowing liquid; the temperature regulating device includes a Peltier element, a first substrate, and a second substrate, wherein the Peltier element is disposed between the first substrate and the second substrate and is respectively bonded and connected to the first substrate and the second substrate; the first substrate is disposed over the opening end of the liquid flow channel and cooperates with the liquid flow channel to form a liquid flow channel for flowing liquid; the Peltier element cools or heats the liquid flowing through the liquid flow channel through the first substrate; the design of this invention simplifies the structure of the constant temperature device, eliminates the heat-conducting plate in the prior art, and allows the temperature regulating device to directly contact the flow guide, thereby allowing the liquid in the liquid flow channel to directly contact the temperature regulating device and exchange heat, effectively reducing the
thermal resistance during the heat exchange process and improving the heat exchange efficiency.