PURPOSE: To secure workability and improve the draining capacity of a drain wall, by guiding a guide member in an existing guide column by use of a easing with the guide member and a drain plate and closely driving the drain plate.

CONSTITUTION: A drain plate 20 is driven close to an existing drain plate together with a easing 10 provided with guide members 12 at both sides. A guide column 30b connected to one of guide members 12 of the casing 10 is inserted in the ground at the same time. Add then the easing is pulled out so as to leave the guide column 30b and the drain plate 20 in the ground. Moreover, the driving position of drain plate 20 is shifted and the above processes are repeated. When driving the casing 10, the other guide member 12 of the easing 10 is driven by the guide of the existing guide column 30. When pulling out the easing 10, the existing guide column 30 is connected to the other guide member 12 of the easing 10. In this way, the draining capacity is improved by a group of drain plates 20 and a drain wall with a high draining capacity can be obtained.