ELECTROCHEMICAL SENSOR, AND SENSOR HEAD

PROBLEM TO BE SOLVED: To provide an electrochemical sensor for measuring a ratio of concentration between two ion species included in a liquid to be measured, capable of enhancing accuracy of measurement and having small size and low-costs.SOLUTION: An electrochemical sensor calculates a drift velocity of a reference solution, showing a drift amount per unit time on the basis of to a drift amount showing deviation following a time lapse between a first potential difference detected at a first time and a second potential difference detected at a second time (S8-2) and performs correction according to the drift velocity so as to dissolve a drift amount generated between the second time and a third time to a third potential difference detected at the third time after the second time to require the corrected third potential difference of a liquid to be measured (S11-2). A ratio of concentration between a first ion species and a second ion species is required according to a difference between the second potential difference of the reference solution and the corrected third potential difference of the liquid to be measured (S12).