A constant temperature device comprising a container for containing liquid, a light source module, a heat transmission channel and a temperature control valve is provided. The light source module is disposed on the container and comprising a plurality of light sources and at least one group of heat conductive fins. The heat transmission channel is connected to the container. The liquid in the container is transmitted out of the container by the heat transmission channel and passes through the heat conductive fins to take away the heat generated by the light sources. After the liquid passes through the heat conductive fins, the heat transmission channel is divided to a first channel and a second channel. The first channel and the second channel are connected to the container, and the second channel comprises at least one group of heat radiating fins. The temperature control valve is disposed in the heat transmission channel to control the liquid to pass through one of the first channel and the second channel.一種恆溫裝置,包括一容置器、一光源模組、一導熱通道以及一溫度控制閥。容置器用以容納液體。光源模組設置於容置器上方,且具有多數個光源及至少一導熱片。導熱通道連接於容置器,容置器中的液體藉由導熱通道導出並通過導熱片,帶走光源產生的熱量。導熱通道在液體通過導熱片後被分為一第一通道與一第二通道,第一通道與第二通道連接容置器,且第二通道包括至少一散熱片。溫度控制閥設置於導熱通道,用以控制液體流入第一通道或第二通道。1‧‧‧容置器2‧‧‧光源模組3‧‧‧導熱通道4‧‧‧溫度控制閥5‧‧‧過濾器6‧‧‧溫度感測器7‧‧‧加熱器11‧‧‧第一表面12‧‧‧第二表面21‧‧‧光源22‧‧‧導熱片31‧‧‧第一通道32‧‧‧第二通道100‧‧‧恆溫裝置321‧‧‧散熱片
