To efficiently perform improvement extending over the wide range of subsoil.

This subsoil improving machine is provided with a guide frame installed in a jobfield, a guide post elevatably moving leader 9 movable in the horizontal direction to the guide frame, a guide post 10 elevatably supported with the leader 9, and a main chain member 19 windingly provided on the outer circumference of the guide post 10 capably of endlessly rotationally moving and projectingly provided with drilling blades 18 on the outer face. It is further provided with a chain member 26 for enlarged drilling windingly provided extending over the required range in the vertical direction on both sides of the lower part of the guide post 10 capably of endlessly rotationally moving and projectingly provided with drilling blades 25 on the outer face.