To allow precise detection of a liquid level, and enable even liquid level detection for a trace sample.

The apparatus comprises a liquid level approach control means 6 for causing an air nozzle 2 to discharge air at least before the air nozzle 2 reaches a liquid level 1 and for relatively moving the air nozzle 2 with respect to the liquid level 1, a reference value determination means 7 for detecting an inner pressure of the air nozzle 2 by means of a pressure sensor 5 before the air nozzle 2 reaches the liquid level and for determining a pressure reference value based on the detected value by the pressure sensor 5, a liquid level discrimination means 8 for comparing the pressure value of the pressure sensor 5 with the pressure reference value determined by the reference value determination means 7 so as to determine that the air nozzle 2 has reached the liquid level 1 provided that the pressure value of the pressure sensor 5 exceeded the pressure reference value, and a stop control means 9 for stopping the air discharge from the air nozzle 2 so as to stop the relative movement of the air nozzle 2 with respect to the liquid level 1 under the conditions where it is determined by means of the liquid level discrimination means 8 that the air nozzle 2 has reached the liquid level 1.