A variable valve driving mechanism is provided with an eccentric member (14) having an annular eccentric portion (15), which is eccentric relative to a camshaft (11), and arranged on an outer periphery of the camshaft (11); an intermediate rotating member (16) having a first groove portion (16A) and second groove portion (16B), which extend in radial directions, and rotatably supported on the eccentric portion (15); a cam lobe (12) having a cam portion (6) for opening and closing an intake valve or exhaust valve (2) and arranged concentrically with and rotatable around the camshaft (11) and for rotation relative to the camshaft (11); a first pin member (17,23) slidably fitted at one end thereof in the first groove portion (16A) and connected at opposite end thereof to the camshaft (11) so that rotation of the camshaft (11) is transmitted to the intermediate rotating member (16); a second pin member (18,24) slidably fitted at one end thereof in the second groove portion (16B) and connected at opposite end thereof to the cam lobe (12) so that rotation of the intermediate rotating member (16) is. transmitted to the camshaft (11); and eccentric position adjusting means (30) for rotating the eccentric member (14) in accordance with a state of operation of the internal combustion engine.