Mobile well drilling apparatus for a drilling site (S) with clustered wells (W), comprising: - a substructure , which lies on the ground and supports the well drilling apparatus ; - a mast comprising: - hinging points ; and - fixing points , said mast being hinged to said substructure via said hinging points , about which said mast is able to rotate in such a way as to move from a substantially horizontal position to a substantially vertical position during the switching of the well drilling apparatus from an assembling configuration to an operating configuration; - a drill floor comprising: - a first portion hinged to said mast ; and - a second portion rigidly fixed to said mast and moving integrally therewith; - a draw-works which is permanently installed on the substructure ; said substructure comprises: - a first sub-base ; and - a second sub-base ; said first sub-base and said second sub-base being arranged parallel to each other and appropriately spaced apart; characterized in that the first portion of the drill floor comprises a connection portion to which a ramp of a catwalk can be connected, allowing said ramp to move integrally with the drilling apparatus ; said connection portion faces towards one of the two sub-bases ; a support structure is adapted to be fixed to such ramp , and at the opposite end said support structure is adapted to be fixed to a single sub-base ; said hinging points of the mast being connected to only one of said first sub-base or said second sub-base ; in the operating configuration of the well drilling apparatus , said fixing points of the mast being respectively connected to that sub-base only, which is opposite to the sub-base to which said hinging points are connected; each one of the two sub-bases comprising at least one pair of hydraulic walking devices ; said walking devices being adapted to move the well drilling apparatus between said clustered wells (W) that are present on the drilling site (S). - a substructure , which lies on the ground and supports the well drilling apparatus ; - a mast comprising: - hinging points ; and - fixing points , said mast being hinged to said substructure via said hinging points , about which said mast is able to rotate in such a way as to move from a substantially horizontal position to a substantially vertical position during the switching of the well drilling apparatus from an assembling configuration to an operating configuration; - hinging points ; and - fixing points , said mast being hinged to said substructure via said hinging points , about which said mast is able to rotate in such a way as to move from a substantially horizontal position to a substantially vertical position during the switching of the well drilling apparatus from an assembling configuration to an operating configuration; - a drill floor comprising: - a first portion hinged to said mast ; and - a second portion rigidly fixed to said mast and moving integrally therewith; - a first portion hinged to said mast ; and - a second portion rigidly fixed to said mast and moving integrally therewith; - a draw-works which is permanently installed on the substructure ; - a first sub-base ; and - a second sub-base ; <EOS>