A sample processing system is configured for analyzing, preprocessing, or carrying out other operations for a biological sample such as blood or urea. With the sample processing system, it is possible to store samples to be stored in a thermally insulated state or specimens required for accuracy control in the thermally insulated state for preventing evaporation or denaturing of the samples and specimens. Also it is possible to carry in or out the samples, rack by rack, according to necessity. Further, the sample processing system is provided with a buffer unit in a cold container having a capability for cold storage and also by accessing a sample rack at random for carrying in or out a rack with a transfer mechanism provided outside of the cold container.