PURPOSE: To exactly measure the water content in soil by providing an enclosure which encloses the outer periphery of a porous cup in the soil by maintaining a prescribed spacing.

CONSTITUTION: A cylindrical body 2 is inserted into the cylindrical enclosure 3 and projects through an annular plug body 5 upward from the enclosure 3 to facilitate the access to a plug body 7 and to facilitate the coupling of a pointer type vacuum gage 8 to the cylindrical body 2. A space is delineated between the bottom end of the porous cup 1 and a bottom cap 4 made of sintered inorg. soil in the part of the enclosure 3 lower than the annular plug body 5. The sintered granular inorg. soil 9 is packed into this space. The water in the vessel passes through the cup 1, penetrates the inorg. soil 9 and the bottom cap 4 and moves successively into the coil by capillarity when the water content in the soil is low. A vacuum state is generated in the cylindrical body 2 and this value can be read by the vacuum gape 8 and, therefore, the water content of the soil can be measured by a PF value if the scale of the vacuum gage 8 is previously formed as a converted scale. Since the cup 1 is enclosed with the enclosure 3 which does not allow the permeation of water, the root entanglement of crops is prevented.