A plunger is moved downwardly in predetermined distance while the tip of the sample probe is immersed in a sample to suck the sample into the probe. A pressure sensor detects the pressure fluctuation during the suction operation, an AD converter converting the signals into digital signals to send the signals for a signal processing unit. The signal processing unit extracts feature variables data of a suction waveform to calculate the Statistical distance from normal group data. The Statistical distance an a threshold value are compared with each other, it is judged that there is an abnormality in the suction operation when the Statistical distance is more than or equal to the threshold value. When the Statistical distance is smaller than the threshold value, an operation is proceeded to a discharge operation.