A device for ensuring continuous circulation in well drilling comprises a tubular body having an axial channel therein, with a lateral opening closed by a removable plug. A flapper valve is placed in the tubular conduit, whose shut-off member is movable between a transverse position, in which it closes the axial channel, and a longitudinal position, in which it closes in a pressure-tight manner the lateral opening. Advantageously, the device comprises magnetic mechanism to operate on the shut-off member in the longitudinal position and retain it in the longitudinal position with a preset load, and as the latter is exceeded the shut-off member may be moved to the transverse position.