PURPOSE: To improve considerably management of measuring accuracy and also to obtain a confirming device simple in constitution and can be handled easily, by moving a light emitting element body and a photodetector body along a passage into which a liquid is sucked, so that a height of a liquid level is detected.

CONSTITUTION: A relation of a moving time (t) extending from the upper limit stop position of a measuring member 21 to a liquid level height, and a liquid quantity corresponding to a suction height of a sample 1, and a light quantity converting voltage value (OV value) of air (a) and the sample 1 are stored in advance in a control device 23, respectively. Subsequently, when the measuring member 21 is made to descend at a constant speed along a passage by starting a driving device 22 in case a measuring light is transmitting through the layer of the air (a), as for the OV value photodetected by a photodetector body 25, a value of about -5V is inputted, and a register R displays '0'. When the member 21 further descends and the measuring light transmits through the inside of the sample 1, a light quantity photodetected by the element body 25 cecreases remarkably, the OV value becomes -2W-3V or so, and the register R displays '1'. Also, by detecting a moving time t1 of the member 21 of until this display is inputted to the device 23, a liquid quantity which is sucked up to a pipet P is confirmed.