A drill head for a rotation drilling rig, including: a rotation motor, a drill head spindle, and a gear change transmission between the rotation motor and the drill head spindle, the gear change transmission including an input shaft connected to the rotation motor and an output shaft connected to the drill head spindle. The input shaft is co-axial with the output shaft, the input shaft is permanently coupled to an intermediate shaft over a first speed reduction gear couple, the gear change transmission) includes a clutch being shiftable between a first position interconnecting the input and output shafts for obtaining the same rotational speed for the input and output shafts, and a second position connecting the intermediate shaft to the output shaft over a second speed reduction gear couple. The invention also relates to a rig.