The Wenner probe provides estimation of the corrosion risk, measuring the specific electric resistance of the concrete near the armature. The probe is equipped with the 4 electrodes: the 2 outer electrodes are supplied with the alternating current of the specified level, and the potential difference is measured at the internal electrodes. It is proportional to the specific electric resistance of the concrete. The probe is fitted with the automatic system of the 4 electrodes wetting, reservoir with water and dosed supply of the fluid. Such design ensures high efficiency of the measurement and ease of operation, providing the fail-safe and rapid wetting of the contact areas of the probe for each new test location.