The invention can be used to secure writing tablets to different types of chairs with legs of different thicknesses and diameters, such that writing tablets can be installed on simple chairs with no armrests. The invention is essentially characterized in that it comprises: a main part having two through-holes therein, namely a first hole for receiving and housing the tubular support of the writing tablet and a second hole dimensioned to be coupled to one of the legs of the chair, and a vertical rod; and a pivoting part connected to the main part by means of the rod, aligned with the second hole and adapted to open and close such that the securing element can be released from the leg of the chair.