<p>A suction cup device includes a cup forming unit (30) cooperating with a flat surface (I) to create a volume-variable space (A), a liftable rod (60) secured to a central portion (31) of the cup forming unit (30), a bracing shell member (20) having a force-transmitting surrounding wall (22) in engagement with a peripheral portion (32) of the cup forming unit (30), and a twistable cap member (40) having a surrounding bottom wall (42) in abutting against a circumferential abutment region (215) of the bracing shell member (20) and threadedly engaged with the liftable rod (60) such that a manually twisted movement of the twistable cap member (40) can result in axial movement of the rod (60) so as to pull the central portion (31) away from the flat surface (I) to produce a reduced pressure in the volume-variable space (A) and a biasing force to thereby ensuring fluid-tight engagement of the cup forming unit (30) with the flat surface (I).</p>
