21 is returned to step 12 in this manner in the present embodiment the actuator section is operated in accordance with a program provided in the processor 100 in response to a detection value detected by each of the detection portions whereby the gravel drain pile is automatically driven if set values of the lower limit value p 1 and upper limit value p 2 are inputted so that the compaction of the ground may be achieved the ground improving method by the gravel drain piles is carried out in the case where only the drain effect of the gravel drain pile is expected the upper and lower limit values may be set to be smaller according to the case where the ground improvement by the gravel drain piles is expected the grain size of crushed stones according to the soil of the subject ground and reaction enough to compact the peripheral ground for the drain piles calculated from the soil and the grain size of crushed stones is provided as a set value the compaction rod tamps the crushed stones in exact quantities in response to the set value and therefore the ground having a predetermined compacting degree is obtained without disconnection of drain piles according to.