PURPOSE: To improve water-retaining property, by a method wherein upper sections are projected from ground and plate units are embeded in parallel with each other, wherein division plates are arranged between the plate units, and wherein a ridge between rice fields which is formed with the plate units and the division plates is filled up with soil.

CONSTITUTION: Two rows of parallel plate units 12 are arranged at adequate intervals, and are embeded so that their upper sections 12a may be projected from ground. Besides, between the two rows of the parallel plate units 12, division plates 13 with cross-sectional areas H are arranged at adequate intervals to form a ridge 11 between rice fields. Then, the ridge 11 between the rice fields which is formed with the plate units 12 and the division plates 13 is filled up with soil 14.