Abstract: The invention concerns a printing mechanism designed for producing an ultra-compact mechanism. The thermal printing mechanism comprises a frame, a motor and a gear assembly driving a roller (7), a thermal printing head (8), a member pressing (9) the head (8) on the roller (7), characterized in that it comprises a member providing at least vertical rigidity (1) to two separate sides of the frame and at least rotational resistance along an axis substantially perpendicular to a third side of the frame, or, at least rotational resistance to two sides of the frame. The invention is useful for printing mechanisms of electronic payment terminals.