1. A method of detecting clogging of a nozzle, comprising the steps of: preparing an aspiration program for driving a pump appropriately depending on a sample to be split and dispensed as aliquots and on the amount of each aliquot; drawing in the sample according to the program; measuring the pressure inside the nozzle; and comparing the measured pressure with threshold values which correspond to aspiration volumes of sample and which are calculated by a method of interpolation from plural threshold values set for plural discrete aspiration volumes, to detect whether the nozzle is clogged or not.