PURPOSE:To high-precisely find an end point of titration in a short time, by a method wherein, from a potential gradient by dropping of titrant and the increase in the potential gradient, a quantity of a next titrant to be dropped is decided, and when the increase in the potential becomes negative, a titration is brought to a stop. CONSTITUTION:When starting a titration, a previously set quantity of titrant is dropped as quantities DELTAV1 and DELTAV2 of an initial titrant into a flask 5 from a self-burette 2. In which case, a microcomputer 11 decides a quantity DELTAV3 of a next titrant, being dropped, from a potential E of liquid to be titrated in the flask 5. Said deciding method finds DELTAV by a formulaI, where A and B are constant, from a change S in the potential E at a time when the quantities DELTAV1 and DELTAV2 of the titrant are dropped and a change DELTAS in the S at a time when the titrant quantities DELTAV1 and DELTAV2 are dropped. Corresponding to the value of the DELTAV, a titrant quantity DELTAV3 is computed by a microcomputer 11 to conduct a measurement. The titration continues, but when a change DELTAS in S' is converted from a positive to a negative, the microcomputer 11 stops the supply of the titrant from the self-burette 2.
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