A device for regulating the height of a cistern flushing mechanism comprising: a long part which is fitted inside an upper base of a main body of the flushing mechanism, so that the long part is regulatable in its axial position and associated with a push mechanism which, in an active position, moves the main body of the flushing mechanism downwards by means of the long part; characterized in that the device further comprises: two facing extensions which emanate from the upper base of the main body and define a conduit wherein the long part fits into; and wherein the facing extensions fit, in turn, inside a circular orifice made up of a tightening part which, in turn, is coupled around the facing extensions; wherein said facing extensions comprise: internal wings in the upper edges of the facing extensions wherein the internal wings face some opposing portions of the long part; and external wings which are in contact with an edge of the orifice of the tightening part; and wherein said tightening part has gyratory mobility around the facing extensions and wherein said tightening part is axially retained between the upper base of the main body and the external wings of the two facing extensions; and wherein the tightening part incorporates two opposing projections which protrude above an upper face of said tightening part; and wherein said opposing projections are located at the height of the external wings of the facing extensions so that: when the long part is in a locking position, the projections of the tightening part press against the external wings, deforming them and causing axial retention of the long part by means of the internal wings of the facing extensions; and when the long part is in a release position, the opposing projections of the tightening part are not in contact with the external wings of the facing extensions. a long part which is fitted inside an upper base of a main body of the flushing mechanism, so that the long part is regulatable in its axial position and associated with a push mechanism which, in an active position, moves the main body of the flushing mechanism downwards by means of the long part; characterized in that the device further comprises: two facing extensions which emanate from the upper base of the main body and define a conduit wherein the long part fits into; and wherein the facing extensions fit, in turn, inside a circular orifice made up of a tightening part which, in turn, is coupled around the facing extensions; wherein said facing extensions comprise: internal wings in the upper edges of the facing extensions wherein the internal wings face some opposing portions of the long part; and external wings which are in contact with an edge of the orifice of the tightening part; and wherein said tightening part has gyratory mobility around the facing extensions and wherein said tightening part is axially retained between the upper base of the main body and the external wings of the two facing extensions; when the long part is in a locking position, the projections of the tightening part press against the external wings, deforming them and causing axial retention of the long part by means of the internal wings of the facing extensions; and when the long part is in a release position, the opposing projections of the tightening part are not in contact with the external wings of the facing extensions.