PURPOSE: To enable calibrations of sensors to be carried out while keeping them in a sterilized condition so as to monitor objective measurement components in real time and continuously with high safety by sterilizing measurement parts, pipings for calibration liquid, pipings for the first and second objective liquids and supply sources of the calibration liquid, beforehand.

CONSTITUTION: Constituents of a sensor part 2, i.e., measurement parts 8, calibration liquid vessels 9, 10, a washing liquid vessel 11, a waste liquid bag 12, pipings 13, 14 for the calibration liquid, a piping 15 for the washing liquid, pipings 16, 18, 20, 21 for blood, pipings 23, 24 for the waste liquid and connectors 17, 19, 22, 44 to 46 are sterilized beforehand. Furthermore, the calibration liquid and the blood are not brought into contact with roller pumps 34, 35 and stop valves 25 to 33, because the roller pumps 34, 35 and stop valves 25 to 33 can transport and stop the calibration liquid or the blood from outsides of respective pipings. It is possible, therefore, to return the blood, which is once took out of a human body P and undergoes measurements, into the body P again and to monitor pH of the blood, etc., in real time and continuously with an improved safety.