Soil Salinity is one of the main environmental factors that have a serious impact on crop production, and soil properties affect plant salt stress. As for the salinity in soil, it is common to measure soil electrical conductivity （EC） with a soil water suspension （1：5） because of its ease of measurement, on the while, another index, ECe is also measured using a saturated soil extract. In this study, NaCl was added to Masa soil （granite base material） with low humus content and CEC, and the comparison and relationship between EC and ECe were examined by a newly developed method. ECe increased even with a slight salinity, and the value was 19 times higher than EC（1：5）. In addition, when tomato was cultivated in Masa soil with four levels of NaCl, the Na concentration in the above-ground part of the tomato increased with the salt concentration, and the K/Na ratio and Ca/Na ratio decreased. Apparent salt damage symptoms were observed at EC 0.6 dS/m（ECe=10.8 dS/m）, and complete mortality at 0.8 dS/m（ECe=20.0 dS/m）, indicating that tomato salt damage is possible to occur in Masa soil. The Na concentration in the upper part of the plant top was higher than that in the lower part and the root. From the above, it appeared that ECe measured with saturated soil extract could detect salt concentration more sensitively and is more effective in predicting salt stress of tomato in Masa soil.