The utility model relates to a medical instrument which is also called to a PCR programmed control automatic circulation instrument. The PCR technique is a natural replication process which simulates DNA (deoxyribonucleic acids). A specimen pool of the utility model adopts a nonisothermal three-pool structure arranged in parallel, and thus, the specimen pool and a freezing bath groove can be additionally arranged optionally. The utility model adopts the method that a mechanical arm is driven by double motors controlled by a computer to move a specimen disk, the mechanical transmission structure of the original device is greatly simplified, and the heat exchanging and the pool exchanging of the specimen are reliable and quick. A single aqueous medium is changed into double mediums, namely, a heat insulating layer which can prevent water content from evaporating is additionally arranged on the water surface, and the problem of oversized space humidity of the instrument is avoided. The utility model has the advantages of complete function and reliable performance, and the utility model can be easily refitted to an automatic piece coloring instrument.