1. A self-propelled drilling rig for boring blastholes and small-diameter wells, said drilling rig comprising: a frame mounted on an undercarriage of said drilling rig; a carriage mounted on said frame; a jib manipulator swingably mounted on said carriage for carrying a feeding mechanism of a boring tool; drive means for moving said jib manipulator in vertical and horizontal directions, said drive means comprising hydraulic cylinders with slide valves; and a servomechanism comprising a hydraulic cylinder mounted on said frame, the movable part of said cylinder being connected to said carriage and the working chambers of said cylinder communicating with a longitudinally movable slide valve and with a hydraulic drive provided with a reduction gear operatively connected to said longitudinally movable slide valve, and a plate being attached to said slide valve, said plate cooperating with a pusher rigidly secured to said jib manipulator.