57 An apparatus for measuring ionic activity is comprised of a rotatable turret (13A) and at least one pair of vertically movable probes (14A). The turret (13A) intermittently conveys slide-type ionic activity measuring devices, one by one, on each of which are spots of reference and sample solutions, to a measuring section where the probes (14A) come into contact with the measuring device so as to measure the potential difference corresponding to the difference in ionic activity of a specific ion between the reference and sample solutions. After measurement the turret (13A) further conveys the device to a discharging section (15) where the device is automatically discharged. The reference solution is preferably dripped through a nozzle (12C) connected to a reservoir (12A) when the measuring device is located at a position below the nozzle (12C).