Mobile well drilling apparatus for a drilling site with clustered wells, 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 (211, 212); 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 (212, 211); 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 (212, 211) only, which is opposite to the sub-base to which said hinging points are connected; each one of the two sub-bases (211, 212) comprising at least one pair of hydraulic walking devices; said walking devices being adapted to move the well drilling apparatus between said clustered wells that are present on the drilling site. - 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;