PURPOSE: To provide a ballast renewal machine of simple construction by a method wherein a screw auger of a specific shape and a vacuum sucking port for recovering small pieces of ballast to be abandoned are provided to recover the small pieces of ballast nearly completely.

CONSTITUTION: While a screw auger 1 is rotating, a ballast renewal machine is advanced. The screw auger 1 excavates ballast below a rail. At the same time, the auger 1 carries excavated ballast from the vicinity of the center of the rail toward the left and right sides of the ballast. A lead angle of the auger 1 is made beforehand larger with distance from the center of the rail, whereby large-sized pieces of ballast which can be regenerated are carried to the left and right sides of ballast. On the other hand, small-pieces of ballast to be abandoned are recovered through a vacuum sucking port 2 at a point midway in the auger 1.