A novel measurement method and a measurement device for measuring chemical oxygen demand (COD) or total organic carbon (TOC) are provided. A counter electrode and a working electrode comprising an electrically-conductive diamond electrode are brought into contact with a test solution containing organic matter; changes in a current that flows between the electrodes when a voltage is applied between the working electrode and the counter electrode are detected; and the quantity of a charge is measured until a detected current value matches a background current value, and the COD or TOC of the test solution is determined from the quantity of the charge that was measured. Furthermore, the measurement device is provided with: a cell in which the counter electrode and the working electrode comprising the electrically-conductive diamond electrode are integrated; a means for applying a voltage between the working electrode and the counter electrode; a means for detecting changes in a current that flows due to said applied voltage; and an information processing means for measuring the quantity of the charge until the detected current value matches the background current value, and for determining the COD or TOC of the test solution from the quantity of the charge that was measured.